{"msg":"第四节 数据库基础","code":200,"data":{"currentIndex":null,"examId":null,"examTime":null,"questionList":[{"id":"794931011342323713","title":"<p><br/></p><p class=\"MsoNormal\" style=\"line-height: 150%;\"><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"><span style=\"font-family:宋体\">数据仓库中数据</span></span><span style=\"text-decoration:underline;\"><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"><span style=\"font-family:宋体\">（</span>40）</span></span><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"><span style=\"font-family:宋体\">的特点是指数据一旦进入数据仓库后，将被长期保留并定期加载和刷新，可以进行各种查询操作，但很少对数据进行修改和删除操作。</span></span><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"></span></p>","analyze":"<p><br/></p><p class=\"MsoNormal\" style=\"text-indent: 21pt; line-height: 150%;\"><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"><span style=\"font-family:宋体\">数据仓库拥有以下四个特点：</span></span><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"></span></p><p class=\"MsoNormal\" style=\"text-indent: 21pt; line-height: 150%;\"><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\">①面向主题：操作型数据库的数据组织面向事务处理任务，各个业务系统之间各自分离，而数据仓库中的数据是按照一定的主题域进行组织。主题是一个抽象的概念，是指用户使用数据仓库进行决策时所关心的重点方面，一个主题通常与多个操作型信息系统相关。</span><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"></span></p><p class=\"MsoNormal\" style=\"text-indent: 21pt; line-height: 150%;\"><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\">②集成性：面向事务处理的操作型数据库通常与某些特定的应用相关，数据库之间相互独立，并且往往是异构的。而数据仓库中的数据是在对原有分散的数据库数据进行抽取、清理的基础上经过系统加工、汇总和整理得到的，必须消除源数据中的不一致性，以保证数据仓库内的信息是关于整个企业的一致的全局信息。</span><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"></span></p><p class=\"MsoNormal\" style=\"text-indent: 21pt; line-height: 150%;\"><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\">③相对稳定性：操作型数据库中的数据通常需要实时更新，数据根据需要及时发生变化。数据仓库的数据主要供企业决策分析之用，所涉及的数据操作主要是数据查询，-旦某个数据进入数据仓库以后，一般情况下将被长期保留，也就是数据仓库中一般有大量的查询操作，但修改和删除操作很少，通常只需要定期的加载、刷新。</span><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"></span></p><p class=\"MsoNormal\" style=\"text-indent: 21pt; line-height: 150%;\"><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\">④反映历史变化：操作型数据库主要关心当前某一个时间段内的数据，而数据仓库中的数据通常包含历史信息，系统记录了企业从过去某一时点(如开始应用数据仓库的时点(到目前的各个阶段的信息，通过这些信息，可以对企业的发展历程和未来趋势做出定量分析和预测。</span><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"></span></p><p class=\"MsoNormal\" style=\"line-height: 150%;\"><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"><span style=\"font-family:宋体\">参考答案：</span></span><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\">(40)</span><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\">C</span><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"></span></p>","multi":0,"questionType":1,"answer":"C","chooseItem":["794931013330423809"],"itemList":[{"id":"794931013208788993","questionId":"794931011342323713","content":"面向主题","answer":0,"chooseValue":"A"},{"id":"794931013225566209","questionId":"794931011342323713","content":"集成性","answer":0,"chooseValue":"B"},{"id":"794931013330423809","questionId":"794931011342323713","content":"相对稳定性","answer":1,"chooseValue":"C"},{"id":"794931013401726977","questionId":"794931011342323713","content":"反映历史变化","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931020183916545","title":"<p><br/></p><p class=\"MsoNormal\"><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">给定关系模式</span>R(A1，A2，A3，A4)，R上的函数依赖集F={A1A3→A2，A2→A3}，</span><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">若将</span>R分解为p={(A1A2)，(A1，A3)}，那么该分解</span><span style=\"text-decoration:underline;\"><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">（</span>43）</span></span><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">。</span></span></p>","analyze":"<p><span style=\"font-family: 宋体; font-size: 10.5pt; text-indent: 21pt;\">A1A3→A2，A2→A3，没有出现A4，所以候选关键字中肯定包A4，属性A1A3A4决定全属性，故为候选关键字。同理A1A2A4也为候选关键字。</span><br/></p><p class=\"MsoNormal\" style=\"text-indent: 21pt; line-height: 150%;\"><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"><span style=\"font-family:宋体\">设</span>U1={A1，A2}，U2={A1，A3}，那么可得出：U1∩U2→(U1-U2)=A1→A2，U1∩U2→(U2-U1)=A1→A3，而A1-A2，A1-A3∉F+，所以分解ρ是有损连接的。</span><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"></span></p><p class=\"MsoNormal\" style=\"line-height: 150%;\"><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"><span style=\"font-family:宋体\">又因为</span>F1=F2=∅， F+≠(F1∪F2)+，所以分解不保持函数依赖。</span><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"></span></p><p class=\"MsoNormal\" style=\"line-height: 150%;\"><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"><span style=\"font-family:宋体\">参考答案：</span></span><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\">(43)</span><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\">D</span><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"></span></p>","multi":0,"questionType":1,"answer":"D","chooseItem":["794931022130073601"],"itemList":[{"id":"794931022088130561","questionId":"794931020183916545","content":"是无损联接的","answer":0,"chooseValue":"A"},{"id":"794931022100713473","questionId":"794931020183916545","content":"是保持函数依赖的","answer":0,"chooseValue":"B"},{"id":"794931022117490689","questionId":"794931020183916545","content":"既是无损联接又保持函数依赖","answer":0,"chooseValue":"C"},{"id":"794931022130073601","questionId":"794931020183916545","content":"既是有损联接又不保持函数依赖","answer":1,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931230687645697","title":"<p>数据仓库不包括（）。</p>","analyze":"<p>数据仓库包括数据源、数据的存储与管理、OLAP 服务器与各种报表工具、查询工具、数据分析工具、数据挖掘工具及各种基于数据仓库或数据集市的应用开发工具。OLTP是传统的关系型数据库联机事务处理过程。</p>","multi":0,"questionType":1,"answer":"C","chooseItem":["794931232570888193"],"itemList":[{"id":"794931232537333761","questionId":"794931230687645697","content":"数据源","answer":0,"chooseValue":"A"},{"id":"794931232554110977","questionId":"794931230687645697","content":"OLAP 服务器","answer":0,"chooseValue":"B"},{"id":"794931232570888193","questionId":"794931230687645697","content":"OLTP 服务器","answer":1,"chooseValue":"C"},{"id":"794931232591859713","questionId":"794931230687645697","content":"报表工具","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931050416459777","title":"<p><span style=\"font-family:宋体\">数据的物理独立性和逻辑独立性分别是通过修改（ </span><span style=\"font-family:宋体\">）来完成的。</span></p><p class=\"MsoNormal\"><br/></p>","analyze":"<p><br/></p><p class=\"MsoNormal\"><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">物理独立性是指的内模式发生变化，只需要调整模式与内模式之间的映像，而不用修改应用程序。</span></span><span style=\"font-family: Calibri; font-size: 10.5pt;\"></span></p><p class=\"MsoNormal\"><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">逻辑独立性是指的模式发生变化，只需要调整外模式与模式之间的映像，而不用修改应用程序。</span></span><span style=\"font-family: Calibri; font-size: 10.5pt;\"></span></p><p class=\"MsoNormal\" style=\"text-indent: 20.7pt;\"><span style=\"font-family: 黑体; font-size: 10.5pt; background: #7F7F7F;\"><span style=\"font-family:黑体\">参考答案</span></span><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">：</span></span><span style=\"font-family: 宋体; font-size: 10.5pt;\">D</span></p>","multi":0,"questionType":1,"answer":"D","chooseItem":["794931052341645313"],"itemList":[{"id":"794931052274536449","questionId":"794931050416459777","content":"外模式与内模式之间的映像、模式与内模式之间的映像","answer":0,"chooseValue":"A"},{"id":"794931052295507969","questionId":"794931050416459777","content":"外模式与内模式之间的映像、外模式与模式之间的映像","answer":0,"chooseValue":"B"},{"id":"794931052320673793","questionId":"794931050416459777","content":"外模式与模式之间的映像、模式与内模式之间的映像","answer":0,"chooseValue":"C"},{"id":"794931052341645313","questionId":"794931050416459777","content":"模式与内模式之间的映像、外模式与模式之间的映像","answer":1,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931008523751425","title":"<p><br/></p><p class=\"MsoNormal\"><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">采用数据仓库技术进行数据收集时，有时会遇一些略微不一致但可以纠正的数据，纠正这些数据的过程称为</span></span><span style=\"text-decoration:underline;\"><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">（</span>23）</span></span><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">。</span></span></p>","analyze":"<p><br/></p><p class=\"MsoNormal\" style=\"text-indent: 21pt; line-height: 150%;\"><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"><span style=\"font-family:宋体\">在采用数据仓库技术进行数据收集时，有时会遇到一些略微不一致但可以纠正的数据，这时需要采用数据清洗技术对这些不一致的数据进行处理和纠正。</span></span><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"></span></p><p class=\"MsoNormal\" style=\"line-height: 150%;\"><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"><span style=\"font-family:宋体\">参考答案：（</span></span><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\">23）</span><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\">C</span><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"></span></p>","multi":0,"questionType":1,"answer":"C","chooseItem":["794931010419576833"],"itemList":[{"id":"794931010390216705","questionId":"794931008523751425","content":"数据转换","answer":0,"chooseValue":"A"},{"id":"794931010406993921","questionId":"794931008523751425","content":"数据抽取","answer":0,"chooseValue":"B"},{"id":"794931010419576833","questionId":"794931008523751425","content":"数据清洗","answer":1,"chooseValue":"C"},{"id":"794931010436354049","questionId":"794931008523751425","content":"数据装载","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931025921724417","title":"<p><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">关系</span>R、S如下表所示，R÷（πA1</span><span style=\"font-family: 宋体; font-size: 10.5pt;\">,</span><span style=\"font-family: 宋体; font-size: 10.5pt;\">A2(σ 1<3(S)))</span><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">，</span>R、S的左外联接、右外联接和完全外联接的元组个数分别为</span><span style=\"text-decoration:underline;\"><span style=\"font-family: 宋体; font-size: 10.5pt;\">(45)</span></span><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">。</span></span><br/></p><p><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\"><img style=\"max-width:100%;height:auto\" src=\"https://image.chaiding.com/ruankao/f3ec86458424dd3a3a3db0179a44014d.png?x-oss-process=style/ruankaodaren\"/></span></span></p>","analyze":"<p><br/></p><p class=\"MsoNormal\" style=\"line-height: 150%;\"><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"><span style=\"font-family:宋体\">关系代数的除法运算是同时从关系的水平方向和垂直方向进行运算的。若给定关系</span><span style=\"font-size: 10.5pt; text-indent: 21pt;\">R(X，Y)和S(Y，Z)，X、Y、Z属性组，R÷S应当满足元组在X上的分量值x的象集Yx包含S在Y上投影的集合。记作：</span><span style=\"font-family:宋体\"><br/></span></span></p><p class=\"MsoNormal\" style=\"line-height: 150%;\"><img style=\"max-width:100%;height:auto\" src=\"https://image.chaiding.com/ruankao/2da293f34d0be3872b2b2f750ec8549b.png?x-oss-process=style/ruankaodaren\"/></p><p class=\"MsoNormal\" style=\"text-indent: 21pt; line-height: 150%;\"><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"><span style=\"font-family:宋体\">其中：</span>Yx为x在R象集，x=tr[X]。且R÷S的结果集的属性组为X。</span><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"></span></p><p class=\"MsoNormal\" style=\"line-height: 150%;\"><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"><span style=\"font-family:宋体\">根据除法定义，</span>X属性为A3，Y属性为(A1,A2)，R÷S应当满足元组在X上的分量值x的象集Yx包含S在Y上投影的集合，所以结果集的属性为A3。属性A3可以取3个值{3，4，7}，其中：3的象集为{(1，2)}，4的象集为{(2，1)，(3，4)}，7的象集为{(4，6)}。</span><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"></span></p><p class=\"MsoNormal\" style=\"text-indent: 21pt; line-height: 150%;\"><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"><span style=\"font-family:宋体\">根据除法定义，本题关系</span>S为（πA1A2(σ 1<3(S))，在属性组Y(A1A2)上的投影为{(2，1)，(3，4)}如下表所示:</span><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"></span></p><p class=\"MsoNormal\" style=\"line-height: 150%;\"><img style=\"max-width:100%;height:auto\" src=\"https://image.chaiding.com/ruankao/9a7a35260b2d09836a0f8afc36ffdd42.png?x-oss-process=style/ruankaodaren\"/></p><p class=\"MsoNormal\" style=\"text-indent: 21pt; line-height: 150%;\"><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"><span style=\"font-family:宋体\">从以上分析可以看出，只有关系</span>R的属性A3的值为4时，其象集包含了关系S在属性组X即(A1,A2)上的投影，所以R÷S={4}。</span><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"></span></p><p class=\"MsoNormal\" style=\"text-indent: 21pt; line-height: 150%;\"><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\">(45)两个关系R和S进行自然连接时，选择两个关系R和S公共属性上相等的元组，去掉重复的属性列构成新关系。在这种情况下，关系R中的某些元组有可能在关系S中不存在公共属性值上相等的元组，造成关系R中这些元组的值在运算时舍弃了；同样关系S中的某些元组也可能舍弃。为此，扩充了关系运算左外联接、右外联接和完全外联接。</span><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"></span></p><p class=\"MsoNormal\" style=\"line-height: 150%;\"><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"><span style=\"font-family:宋体\">左外联接是指</span>R与S进行自然连接时，只把A中舍弃的元组放到新关系中。</span><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"></span></p><p class=\"MsoNormal\" style=\"line-height: 150%;\"><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"><span style=\"font-family:宋体\">右外联接是指</span>R与S进行自然连接时，只把S中舍弃的元组放到新关系中。</span><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"></span></p><p class=\"MsoNormal\" style=\"line-height: 150%;\"><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"><span style=\"font-family:宋体\">完全外联接是指</span>R与S进行自然连接时，把尺和^中舍弃的元组都放到新关系中。</span></p><p class=\"MsoNormal\" style=\"line-height: 150%;\"></p><p class=\"MsoNormal\" style=\"line-height: 150%;\"><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"><span style=\"font-family:宋体\">从运算的结果可以看出</span>R与S的左外联接、右外联接和完全外联接的元组个数分别为2，2，6</span><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"></span></p><p class=\"MsoNormal\" style=\"line-height: 150%;\"><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"><span style=\"font-family:宋体\">参考答案：</span></span><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\">(45)B</span><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"></span></p>","multi":0,"questionType":1,"answer":"B","chooseItem":["794931028006293505"],"itemList":[{"id":"794931027989516289","questionId":"794931025921724417","content":"2,2,4","answer":0,"chooseValue":"A"},{"id":"794931028006293505","questionId":"794931025921724417","content":"2,2,6","answer":1,"chooseValue":"B"},{"id":"794931028018876417","questionId":"794931025921724417","content":"4,4,4","answer":0,"chooseValue":"C"},{"id":"794931028039847937","questionId":"794931025921724417","content":"4,4,6","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931150475776001","title":"在数据库设计的需求分析阶段，业务流程一般采用（）表示。","analyze":"在数据库设计的需求分析阶段，参与需求分析的主要人员是分析人员和用户，由于数据库应用系统是面向企业和部门的 具体业务，分析人员一般并不了解，而同样用户也不会具有系统分析的能力，这就需要双方进行有效的沟通，使得设计 人员对用户的各项业务了解和熟悉，进行分析和加工，将用户的业务转换成为设计人员所需要的信息组织，即以规范化 的方式进行整理，形成对业务流程描述的文档数据流图和数据描述的文档数据字典，故选项A正确；E-R图是概念设计阶 段的文档，故选项B错误：程序结构图和功能模块图是应用程序设计阶段的文档，不是数据库设计的需求分析阶段的文 档，故选项C、D错误。","multi":0,"questionType":1,"answer":"A","chooseItem":["794931152329658369"],"itemList":[{"id":"794931152329658369","questionId":"794931150475776001","content":"数据流图","answer":1,"chooseValue":"A"},{"id":"794931152346435585","questionId":"794931150475776001","content":"E-R 图","answer":0,"chooseValue":"B"},{"id":"794931152363212801","questionId":"794931150475776001","content":"程序结构图","answer":0,"chooseValue":"C"},{"id":"794931152379990017","questionId":"794931150475776001","content":"功能模块图","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931103247912961","title":"在数据仓库中，数据（ ）是指数据一旦进入数据仓库后，将被长期保留并定期加载和刷新，可以进行各种查询操作，但很少对数据进行修改和删除操作。","analyze":"<p>数据仓库的4大特点如下。</p><p>（1） 面向主题：数据按主题组织。</p><p>（2） 集成的：消除了源数据中的不一致性，提供整个企业的一致性全局信息。</p><p>（3） 相对稳定的：主要进行查询操作，只有少量的修改和删除操作（或无删除）。</p><p>（4） 反映历史变化：记录了从过去某一时刻到当前各个阶段的信息，可对发展历程和未来趋势做定量分析和预测。</p>","multi":0,"questionType":1,"answer":"C","chooseItem":["794931105189875713"],"itemList":[{"id":"794931105118572545","questionId":"794931103247912961","content":"面向主题","answer":0,"chooseValue":"A"},{"id":"794931105152126977","questionId":"794931103247912961","content":"集成性","answer":0,"chooseValue":"B"},{"id":"794931105189875713","questionId":"794931103247912961","content":"相对稳定性","answer":1,"chooseValue":"C"},{"id":"794931105215041537","questionId":"794931103247912961","content":"反映历史变化","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931227869073409","title":"为了更加灵活地运用中断，计算机采用中断屏蔽技术，下列描述错误的是（ ）。","analyze":"<p>为了更加灵活地运用中断，计算机中采用中断屏蔽技术。屏蔽的基本意思是让某种中断不起作用。即对每个外部硬件中断源设置一个中断屏蔽位，约定该位为0时处于开屏蔽状态，为1时处于屏蔽状态。中断源在对应的中断屏蔽位为屏蔽状态时，它的中断请求不能得到 CPU的响应，或者干脆就不能向CPU提出中断请求。</p><p>一般中断控制器是将中断屏蔽位集中在一起，构成中断屏蔽寄存器。中断一般可以分为两类∶不可屏蔽中断和可屏蔽中断。不可屏蔽中断一旦提出请求，CPU必须无条件响应;而对于可屏蔽中断，CPU可以响应，也可以不响应。CPU一般设置两根中断请求输入线，可屏蔽中断输入线INTR和不可屏蔽中断请求 NM。</p><p>对于可屏蔽中断，除了受本身的屏蔽位控制外，还受到 CPU标志寄存器中的中断允许标志位控制。</p><p>典型的非屏蔽中断源的例子是电源掉电，一旦出现，必须立即无条件地响应，否则进行其他任何工作都没有意义。典型的可屏蔽中断如打印机中断。</p>","multi":0,"questionType":1,"answer":"C","chooseItem":["794931229752315905"],"itemList":[{"id":"794931229722955777","questionId":"794931227869073409","content":"一般中断控制器将中断屏蔽位集中在一起，构成中断屏蔽寄存器","answer":0,"chooseValue":"A"},{"id":"794931229739732993","questionId":"794931227869073409","content":"不可屏蔽中断一旦提出请求，CPU 必须无条件响应","answer":0,"chooseValue":"B"},{"id":"794931229752315905","questionId":"794931227869073409","content":"对可屏蔽中断，仅受本身屏蔽位控制，而不受 CPU中断允许标志位控制","answer":1,"chooseValue":"C"},{"id":"794931229769093121","questionId":"794931227869073409","content":"中断源在对应的中断屏蔽位为屏蔽状态时，其中断请求不能被 CPU 响应","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931064828088321","title":"<p><span style=\"font-family:宋体\">某公司数据库中的元件关系模式为</span><span style=\"font-family: 宋体; font-size: 10.5pt;\">P</span><span style=\"font-family:宋体\">（元件号，元件名称，供应商，供应商所在地，库存量），函数依赖集</span><span style=\"font-family:Calibri\">F</span><span style=\"font-family:宋体\">如下所示：</span><br/></p><p class=\"MsoNormal\" style=\"margin-left:0.0000pt;mso-para-margin-left:0.0000gd;text-indent:0.0000pt;mso-char-indent-count:0.0000;\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:Calibri;mso-hansi-font-family:Calibri;mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"> F={<span style=\"font-family:宋体\">元件号→元件名称，（元件号，供应商）→库存量，供应商→供应商所在地</span><span style=\"font-family:Calibri\">}</span></span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:Calibri;mso-hansi-font-family:Calibri;mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">，</span></span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:Calibri;mso-hansi-font-family:Calibri;mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">元件关系的主键为</span></span><span style=\"font-family: 宋体; font-size: 14px;\">元件号，供应商</span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:Calibri;mso-hansi-font-family:Calibri;mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">，该关系存在冗余以及插入异常和删除异常等问题。为了解决这一问题需要将元件关系分解</span></span><span style=\"font-family:宋体\">元件</span><span style=\"font-family:Calibri\">1</span><span style=\"font-family:宋体\">（元件号，元件名称）、元件</span><span style=\"font-family:Calibri\">2</span><span style=\"font-family:宋体\">（元件号，供应商，库存量）、元件</span><span style=\"font-family:Calibri\">3</span><span style=\"font-family:宋体\">（供应商，供应商所在地）</span><span style=\"font-size: 10.5pt;\"><span style=\"font-family:宋体\">，分解后的关系模式可以达到（</span><span style=\"font-family:Calibri\"> </span><span style=\"font-family:宋体\">）。</span></span></p><p class=\"MsoNormal\"><br/></p>","analyze":"<p><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">元</span></span><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">件关系存在非主属性对</span></span><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">码</span></span><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">的部分函数依赖：（</span></span><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">元</span></span><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">件号，供应商）供应商所在地，但是供应商</span>→供应商所在地，故原关系模式</span><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">元</span></span><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">件非</span>2NF<span style=\"font-family:宋体\">的。分解后的关系模式</span></span><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">元</span></span><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">件</span>1<span style=\"font-family:宋体\">、</span></span><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">元</span></span><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">件</span>2<span style=\"font-family:宋体\">和</span></span><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">元</span></span><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">件</span>3<span style=\"font-family:宋体\">消除了非主属性对码的部分函数依赖，同时不存在传递依赖，故达到</span><span style=\"font-family:Calibri\">3NF</span><span style=\"font-family:宋体\">。</span></span><br/></p><p class=\"MsoNormal\"><span style=\"font-family: Calibri; font-size: 10.5pt;\"></span></p>","multi":0,"questionType":1,"answer":"C","chooseItem":["794931066740690945"],"itemList":[{"id":"794931066702942209","questionId":"794931064828088321","content":"1NF","answer":0,"chooseValue":"A"},{"id":"794931066723913729","questionId":"794931064828088321","content":"2NF","answer":0,"chooseValue":"B"},{"id":"794931066740690945","questionId":"794931064828088321","content":"3NF","answer":1,"chooseValue":"C"},{"id":"794931066757468161","questionId":"794931064828088321","content":"4NF","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931241945157633","title":"<p>数据库的安全机制中，通过提供 （ ） 供第三方开发人员调用进行数据更新，从而保证数据库的关系模式不被第三方所获取。</p>","analyze":"<p>存储过程是数据库所提供的一种数据库对象，通过存储过程定义一段代码，提供给应用程序调用来执行。从安全性的角度考虑，更新数据时，通过提供存储过程让第三方调用，将需要更新的数据传入存储过程，而在存储过程内部用代码分别对需要的多个表进行更新，从而避免了向第三方提供系统的表结构，保证了系统的数据安全。</p>","multi":0,"questionType":1,"answer":"C","chooseItem":["794931244012949505"],"itemList":[{"id":"794931243941646337","questionId":"794931241945157633","content":"索引","answer":0,"chooseValue":"A"},{"id":"794931243979395073","questionId":"794931241945157633","content":"视图","answer":0,"chooseValue":"B"},{"id":"794931244012949505","questionId":"794931241945157633","content":"存储过程","answer":1,"chooseValue":"C"},{"id":"794931244042309633","questionId":"794931241945157633","content":"触发器","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931100412563457","title":"<p>在关系R(A1, A2, A3)和S(A2, A3, A4)上进行关系运算的4个等价的表达式E1、E2、E3、E4，如下所示：</p><p><img style=\"max-width:100%;height:auto\" src=\"https://image.chaiding.com/ruankao/51f94c903fb711b4362b959b33feeee6.jpg?x-oss-process=style/ruankaodaren\" title=\"51f94c903fb711b4362b959b33feeee6.jpg\" alt=\"1.jpg\"/></p><p>如果严格按照表达式运算顺序执行，则查询效率最高的是表达式（ ）。</p>","analyze":"<p>本题考查关系代数运行效率问题，解决这类问题有一个通用原则，即存在连接操作与选择操作的尽可能早地完成选择操作。这样能降低参与连接操作的数据量，极大提升运算效率。</p>","multi":0,"questionType":1,"answer":"B","chooseItem":["794931102283223041"],"itemList":[{"id":"794931102270640129","questionId":"794931100412563457","content":"E1","answer":0,"chooseValue":"A"},{"id":"794931102283223041","questionId":"794931100412563457","content":"E2","answer":1,"chooseValue":"B"},{"id":"794931102304194561","questionId":"794931100412563457","content":"E3","answer":0,"chooseValue":"C"},{"id":"794931102320971777","questionId":"794931100412563457","content":"E4","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931044645097473","title":"<p><br/></p><p class=\"MsoNormal\"><span style=\"mso-spacerun:'yes';font-family:宋体;font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">销售公司数据库中的关系零件为</span>P(Pno,Pname,Sname,City,Qty)，Pno表示零件号，Pname表示零件名称，Sname表示供应商，City表示所在地，Qty表示库存量。其函数依赖集F={Pno→Pname，(Pno,Sname)→Qty，Sname→City}。</span><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">关系</span>P</span><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">存在冗余度大、修改操作不一致、插入异常和删除异常的问题。</span></span><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">若将</span>P分解为</span><span style=\"text-decoration:underline;\"><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">（</span>45）</span></span><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">，则可以解决这一问题。</span></span></p>","analyze":"<p><br/></p><p class=\"MsoNormal\" style=\"margin-left: 0pt; text-indent: 21pt; line-height: 150%;\"><span style=\"mso-spacerun:'yes';font-family:宋体;line-height:150%;font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">原零件关系</span>P存在非主属性对码的部分函数依赖：（Pno, Sname) —>Qty,但是Pno ——>Pname、Sname —>City,因此P∈1NF，而非2NF的。1NF主要存在冗余变大、修改操作的不一致、插入异常和删除异常的问题。</span><span style=\"mso-spacerun:'yes';font-family:宋体;line-height:150%;font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p><p class=\"MsoNormal\" style=\"margin-left: 0pt; text-indent: 21pt; line-height: 150%;\"><span style=\"mso-spacerun:'yes';font-family:宋体;line-height:150%;font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">分解后的关系模式</span>P1P2和P3消除了非主属性对码的部分函数依赖，同时不存在传递依赖，故达到3NF。</span><span style=\"mso-spacerun:'yes';font-family:宋体;line-height:150%;font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p><p class=\"MsoNormal\" style=\"margin-left: 0pt; text-indent: 0pt; line-height: 150%;\"><span style=\"font-family: 宋体; font-size: 10.5pt; background: #7F7F7F;\"><span style=\"font-family:宋体\">参考答案</span></span><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">：</span></span><span style=\"font-family: 宋体; font-size: 10.5pt;\">（46）C</span><span style=\"font-family: 宋体; font-size: 10.5pt;\"></span></p>","multi":0,"questionType":1,"answer":"C","chooseItem":["794931046603837441"],"itemList":[{"id":"794931046524145665","questionId":"794931044645097473","content":"P1(Pname,Qty)、P2(Pno,Sname,City)","answer":0,"chooseValue":"A"},{"id":"794931046561894401","questionId":"794931044645097473","content":"P1(Pname,Pname)、P2(Sname,City,Qty)","answer":0,"chooseValue":"B"},{"id":"794931046603837441","questionId":"794931044645097473","content":"P1(Pno,Pname)、P2(Pno,Sname,Qty)、P3(Sname,City)","answer":1,"chooseValue":"C"},{"id":"794931046629003265","questionId":"794931044645097473","content":"P1(Pno,Pname)、P2(Pno,Qty)、P3(Sname,City)、P4(City,Qty)","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931277395415041","title":"数据库的安全机制中，通过提供 () 供第三方开发人员调用进行数据更新，从而保证数据库的关系模式不被第三方所获取。","analyze":"<p>本题考查数据库安全性的基础知识。</p><p>存储过程是数据库所提供的一种数据库对象，通过存储过程定义一段代码，提供给应用程序调用来执行。从安全性的角度考虑，更新数据时，通过提供存储过程让第三方调用，将需要更新的数据传入存储过程，而在存储过程内部用代码分别对需要的多个表进行更新，从而避免了向第三方提供系统的表结构，保证了系统的数据安全。</p>","multi":0,"questionType":1,"answer":"C","chooseItem":["794931279484178433"],"itemList":[{"id":"794931279438041089","questionId":"794931277395415041","content":"索引","answer":0,"chooseValue":"A"},{"id":"794931279463206913","questionId":"794931277395415041","content":"视图","answer":0,"chooseValue":"B"},{"id":"794931279484178433","questionId":"794931277395415041","content":"存储过程","answer":1,"chooseValue":"C"},{"id":"794931279505149953","questionId":"794931277395415041","content":"触发器","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931032649388033","title":"<p><br/></p><p class=\"MsoNormal\"><span style=\"mso-spacerun:'yes';font-family:宋体;font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">在数据库系统中，</span></span><span style=\"mso-spacerun:'yes';font-family:宋体;font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">数据的物理独立性和数据的逻辑独立性是分别通过修改</span></span><span style=\"text-decoration:underline;\"><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">（</span>41）</span></span><span style=\"mso-spacerun:'yes';font-family:宋体;font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">来完成的。</span></span></p>","analyze":"<p><br/></p><p class=\"MsoNormal\" style=\"margin-left: 0pt; text-indent: 21pt; line-height: 150%;\"><span style=\"mso-spacerun:'yes';font-family:宋体;line-height:150%;font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">数据库通常采用三级模式结构，其中，视图对应外模式、基本表对应模式、存储文件对应内模式。</span></span><span style=\"mso-spacerun:'yes';font-family:宋体;line-height:150%;font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p><p class=\"MsoNormal\" style=\"margin-left: 0pt; text-indent: 21pt; line-height: 150%;\"><span style=\"mso-spacerun:'yes';font-family:宋体;line-height:150%;font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">数据的独立性是由</span>DBMS的二级映像功能来保证的。数据的独立性包括数据的物理独立性和数据的逻辑独立性。数据的物理独立性是指当数据库的内模式发生改变时，数据的逻辑结构不变。为了保证应用程序能够正确执行，需要通过修改概念模式与内模式之间的映像。数据的逻辑独立性是指用户的应用程序与数据库的逻辑结构是相互独立的。数据的逻辑结构发生变化后，用户程序也可以不修改。但是，为了保证应用程序能够正确执行，需要修改外模式与概念模式之间的映像。</span><span style=\"mso-spacerun:'yes';font-family:宋体;line-height:150%;font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p><p class=\"MsoNormal\" style=\"margin-left: 0pt; text-indent: 0pt; line-height: 150%;\"><span style=\"font-family: 宋体; font-size: 10.5pt; background: #7F7F7F;\"><span style=\"font-family:宋体\">参考答案</span></span><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">：</span></span><span style=\"font-family: 宋体; font-size: 10.5pt;\">（41）A</span><span style=\"font-family: 宋体; font-size: 10.5pt;\"></span></p>","multi":0,"questionType":1,"answer":"A","chooseItem":["794931034880757761"],"itemList":[{"id":"794931034880757761","questionId":"794931032649388033","content":"模式与内模式之间的映像、外模式与模式之间的映像","answer":1,"chooseValue":"A"},{"id":"794931034905923585","questionId":"794931032649388033","content":"外模式与内模式之间的映像、外模式与模式之间的映像","answer":0,"chooseValue":"B"},{"id":"794931034922700801","questionId":"794931032649388033","content":"外模式与模式之间的映像、模式与内模式之间的映像","answer":0,"chooseValue":"C"},{"id":"794931034939478017","questionId":"794931032649388033","content":"外模式与内模式之间的映像、模式与内模式之间的映像","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931239114002433","title":"<p>在设计关系模式时，有时为了提高数据操作的性能，会故意增加冗余数据，使得关系模式不满足 3NF 或 BCNF，这种方法称之为反规范化，下列不属于反规范化手段的是（）。</p>","analyze":"<p>在设计关系模式时，有时为了提高数据操作的性能，会故意增加冗余数据，使得关系模式不满足 3NF或 BCNF，这种方法称之为反规范化。</p><p>常见的范规范化手段有增加冗余属性、增加派生属性、合并模式和分割模式等。</p>","multi":0,"questionType":1,"answer":"C","chooseItem":["794931240980467713"],"itemList":[{"id":"794931240946913281","questionId":"794931239114002433","content":"合并模式","answer":0,"chooseValue":"A"},{"id":"794931240963690497","questionId":"794931239114002433","content":"增加冗余属性","answer":0,"chooseValue":"B"},{"id":"794931240980467713","questionId":"794931239114002433","content":"创建视图","answer":1,"chooseValue":"C"},{"id":"794931240997244929","questionId":"794931239114002433","content":"增加派生属性","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931041746833409","title":"<p><br/></p><p class=\"MsoNormal\"><span style=\"font-family: 宋体; font-size: 10.5pt;\"> </span><span style=\"font-family: 宋体; font-size: 10.5pt; mso-spacerun: "yes"; mso-font-kerning: 1.0000pt;\"><span style=\"font-family: 宋体;\">销售公司数据库中的关系零件为</span>P(Pno,Pname,Sname,City,Qty)，Pno表示零件号，Pname表示零件名称，Sname表示供应商，City表示所在地，Qty表示库存量。其函数依赖集F={Pno→Pname，(Pno,Sname)→Qty，Sname→City}。关系P为</span><span style=\"text-decoration: underline;\"><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family: 宋体;\">（</span>44）。</span></span></p>","analyze":"<p><br/></p><p class=\"MsoNormal\" style=\"line-height: 150%; text-indent: 21pt; margin-left: 0pt;\"><span style=\"line-height: 150%; font-family: 宋体; font-size: 10.5pt; mso-spacerun: "yes"; mso-font-kerning: 1.0000pt;\"><span style=\"font-family: 宋体;\">原零件关系</span>P存在非主属性对码的部分函数依赖：（Pno, Sname) —>Qty,但是Pno ——>Pname、Sname —>City,因此P∈1NF，而非2NF的。1NF主要存在冗余变大、修改操作的不一致、插入异常和删除异常的问题。</span><span style=\"line-height: 150%; font-family: 宋体; font-size: 10.5pt; mso-spacerun: "yes"; mso-font-kerning: 1.0000pt;\"></span></p><p class=\"MsoNormal\" style=\"line-height: 150%; text-indent: 21pt; margin-left: 0pt;\"><span style=\"line-height: 150%; font-family: 宋体; font-size: 10.5pt; mso-spacerun: "yes"; mso-font-kerning: 1.0000pt;\"><span style=\"font-family: 宋体;\">分解后的关系模式</span>P1P2和P3消除了非主属性对码的部分函数依赖，同时不存在传递依赖，故达到3NF。</span><span style=\"line-height: 150%; font-family: 宋体; font-size: 10.5pt; mso-spacerun: "yes"; mso-font-kerning: 1.0000pt;\"></span></p><p class=\"MsoNormal\"><span style=\"background: #7F7F7F; font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family: 宋体;\">参考答案</span></span><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family: 宋体;\">：</span></span><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family: 宋体;\">（</span></span><span style=\"font-family: 宋体; font-size: 10.5pt;\">45）A </span></p>","multi":0,"questionType":1,"answer":"A","chooseItem":["794931043625881601"],"itemList":[{"id":"794931043625881601","questionId":"794931041746833409","content":"1NF","answer":1,"chooseValue":"A"},{"id":"794931043663630337","questionId":"794931041746833409","content":"2NF","answer":0,"chooseValue":"B"},{"id":"794931043692990465","questionId":"794931041746833409","content":"3NF","answer":0,"chooseValue":"C"},{"id":"794931043726544897","questionId":"794931041746833409","content":"4NF","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931059094474753","title":"<p><span style=\"font-family:宋体;font-family: 宋体; font-size: 10.5pt;\">某公司数据库中的元件关系模式为</span><span style=\"font-family: 宋体; font-size: 10.5pt;\">P</span><span style=\"font-family:宋体;font-family: 宋体; font-size: 10.5pt;\">（元件号，元件名称，供应商，供应商所在地，库存量），函数依赖集</span><span style=\"font-family:Calibri;font-size: 10.5pt;\">F</span><span style=\"font-family:宋体;font-family: 宋体; font-size: 10.5pt;\">如下所示：</span><br/></p><p class=\"MsoNormal\" style=\"margin-left:0.0000pt;mso-para-margin-left:0.0000gd;text-indent:0.0000pt;mso-char-indent-count:0.0000;\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:Calibri;mso-hansi-font-family:Calibri;mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"> F={<span style=\"font-family:宋体\">元件号→元件名称，（元件号，供应商）→库存量，供应商→供应商所在地</span><span style=\"font-family:Calibri\">}</span></span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:Calibri;mso-hansi-font-family:Calibri;mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">，</span></span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:Calibri;mso-hansi-font-family:Calibri;mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">元件关系的主键为（ </span><span style=\"font-family:宋体\">）。</span></span></p>","analyze":"<p><br/></p><p>元件号和供应商的组合键能推导出该关系模式的所有属性，因此为主键。<br/></p><p><br/></p>","multi":0,"questionType":1,"answer":"B","chooseItem":["794931060977717249"],"itemList":[{"id":"794931060960940033","questionId":"794931059094474753","content":"元件号，元件名称","answer":0,"chooseValue":"A"},{"id":"794931060977717249","questionId":"794931059094474753","content":"元件号，供应商","answer":1,"chooseValue":"B"},{"id":"794931060990300161","questionId":"794931059094474753","content":"元件号，供应商所在地","answer":0,"chooseValue":"C"},{"id":"794931061002883073","questionId":"794931059094474753","content":"供应商，供应商所在地","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931205257580545","title":"<p>数据库的安全机制中，通过提供 ( ) 供第三方开发人员调用进行数据更新，从而保证数据库的关系模式不被第三方所获取。</p>","analyze":"<p>本题考查数据库安全性的基础知识。</p><p>存储过程是数据库所提供的一种数据库对象，通过存储过程定义一段代码，提供给应用程序调用来执行。从安全性的角度考虑，更新数据时，通过提供存储过程让第三方调用，将需要更新的数据传入存储过程，而在存储过程内部用代码分别对需要的多个表进行更新，从而避免了向第三方提供系统的表结构，保证了系统的数据安全。</p>","multi":0,"questionType":1,"answer":"C","chooseItem":["794931207153405953"],"itemList":[{"id":"794931207115657217","questionId":"794931205257580545","content":"索引","answer":0,"chooseValue":"A"},{"id":"794931207132434433","questionId":"794931205257580545","content":"视图","answer":0,"chooseValue":"B"},{"id":"794931207153405953","questionId":"794931205257580545","content":"存储过程","answer":1,"chooseValue":"C"},{"id":"794931207165988865","questionId":"794931205257580545","content":"触发器","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931076458893313","title":"<p><span style=\"font-family: 宋体; font-size: 10.5pt;\">在分布式数据库中有分片透明、复制透明、位置透明和逻辑透明等基本概念，其中：</span><br/></p><p class=\"MsoNormal\" style=\"text-indent:20.7000pt;\"><span style=\"text-decoration:underline;\"><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">（ </span></span></span><span style=\"text-decoration:underline;\"><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">）</span></span></span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:Calibri;mso-hansi-font-family:Calibri;mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">是指用户或应用程序不需要知道逻辑上访问的表具体是如何分块存储的。</span></span><span style=\"mso-spacerun:'yes';font-family:Calibri;mso-fareast-font-family:宋体;mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p>","analyze":"<p><span style=\"font-family: 宋体; font-size: 10.5pt; text-indent: 20.7pt;\">本题考查分布式数据库基本概念。分片透明是指用户或应用程序不需要知道逻辑上访问的表具体是怎么分块存储的。复制透明是指采用复制技术的分布方法，用户不需要知道数据是复制到哪些节点，如何复制的。位置透明是指用户无须知道数据存放的物理位置，逻辑透明，即局部数据模型透明，是指用户或应用程序无须知道局部场地使用的是哪种数据模型。</span><br/></p><p class=\"MsoNormal\" style=\"text-indent:20.7000pt;\"><span style=\"mso-spacerun:'yes';font-family:Calibri;mso-fareast-font-family:宋体;mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p>","multi":0,"questionType":1,"answer":"A","chooseItem":["794931078337941505"],"itemList":[{"id":"794931078337941505","questionId":"794931076458893313","content":"分片透明","answer":1,"chooseValue":"A"},{"id":"794931078363107329","questionId":"794931076458893313","content":"复制透明","answer":0,"chooseValue":"B"},{"id":"794931078388273153","questionId":"794931076458893313","content":"位置透明","answer":0,"chooseValue":"C"},{"id":"794931078409244673","questionId":"794931076458893313","content":"逻辑透明","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931196785086465","title":"在某学校的综合管理系统设计阶段，教师实体在学籍管理子系统中被称为"教师"，而在人事管理子系统中被称为"职工"，这类冲突被称之为（25）。","analyze":"<p>在将局部ER图合成全局ER图的过程中需要消除冲突。冲突主要有：</p><p>属性冲突：</p><p>--属性域冲突：不同学校编码方式不同</p><p>--属性值冲突：重量采用千克、磅</p><p>结构冲突：</p><p>--同一对象在不同应用中的抽象不同：</p><p>职工在某一应用中是实体，在另一应用中是属性。</p><p>--同一实体在不同ER图中属性工人数和排列次序不同</p><p>命名冲突：</p><p>--同名异义</p><p>--异名同义</p><p>题干表述属于异名同义的命名冲突。</p>","multi":0,"questionType":1,"answer":"B","chooseItem":["794931198697689089"],"itemList":[{"id":"794931198680911873","questionId":"794931196785086465","content":"语义冲突","answer":0,"chooseValue":"A"},{"id":"794931198697689089","questionId":"794931196785086465","content":"命名冲突","answer":1,"chooseValue":"B"},{"id":"794931198714466305","questionId":"794931196785086465","content":"属性冲突","answer":0,"chooseValue":"C"},{"id":"794931198727049217","questionId":"794931196785086465","content":"结构冲突","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931038693380097","title":"<p><br/></p><p class=\"MsoNormal\"><span style=\"mso-spacerun:'yes';font-family:宋体;font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">给定关系模式</span>R(U,F)，U={A,B,C,D}，F={AB→C,CD→B}。关系R</span><span style=\"mso-spacerun:'yes';font-family:宋体;font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">有</span></span><span style=\"text-decoration:underline;\"><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">（</span>43）</span></span><span style=\"mso-spacerun:'yes';font-family:宋体;font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">。</span></span></p>","analyze":"<p><br/></p><p class=\"MsoNormal\" style=\"margin-left: 0pt; text-indent: 21pt; line-height: 150%;\"><span style=\"mso-spacerun:'yes';font-family:宋体;line-height:150%;font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">根据函数依赖定义，可知</span>ACD→U ,ABD→U,所以ACD和ABD均为候选关键字。</span><span style=\"mso-spacerun:'yes';font-family:宋体;line-height:150%;font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p><p class=\"MsoNormal\" style=\"margin-left: 0pt; text-indent: 0pt; line-height: 150%;\"><span style=\"mso-spacerun:'yes';font-family:宋体;line-height:150%;font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">根据主属性的定义</span>“包含在任何一个候选码中的属性叫做主属性(Prime attribute), 否则叫做非主属性（Nonprime attribute)”，所以，关系R中的4个属性都是主属性。</span><span style=\"mso-spacerun:'yes';font-family:宋体;line-height:150%;font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p><p class=\"MsoNormal\" style=\"margin-left: 0pt; text-indent: 0pt; line-height: 150%;\"><span style=\"font-family: 宋体; font-size: 10.5pt; background: #7F7F7F;\"><span style=\"font-family:宋体\">参考答案</span></span><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">：</span></span><span style=\"font-family: 宋体; font-size: 10.5pt;\">（43）A</span><span style=\"font-family: 宋体; font-size: 10.5pt;\"></span></p>","multi":0,"questionType":1,"answer":"A","chooseItem":["794931040769560577"],"itemList":[{"id":"794931040769560577","questionId":"794931038693380097","content":"0个非主属性和4个主属性","answer":1,"chooseValue":"A"},{"id":"794931040790532097","questionId":"794931038693380097","content":"1个非主属性和3个主属性","answer":0,"chooseValue":"B"},{"id":"794931040803115009","questionId":"794931038693380097","content":"2个非主属性和2个主属性","answer":0,"chooseValue":"C"},{"id":"794931040824086529","questionId":"794931038693380097","content":"3个非主属性和1个主属性","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931047551750145","title":"<p><span style=\"text-indent: 20.7pt; font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">某医院预约系统的部分需求为：患者可以查看医院发布的专家特长介绍及其就诊时间：系统记录患者信息，患者预约特定时间就诊。</span></span><span style=\"text-indent: 20.7pt; font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">用</span> ERD<span style=\"font-family:宋体\">对其进行数据建模时，患者是（ </span></span><span style=\"text-indent: 20.7pt; font-family: 宋体; font-size: 10.5pt;\"> <span style=\"font-family:宋体\">）</span></span></p><p class=\"MsoNormal\"><br/></p>","analyze":"<p><br/></p><p class=\"MsoNormal\"><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">按对于数据流图来说，患者属于外部实体；对于实体关系图来说，患者属于实体。</span></span><span style=\"font-family: 宋体; font-size: 10.5pt;\"></span></p><p class=\"MsoNormal\"><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">选项</span>D<span style=\"font-family:宋体\">的弱实体是指某些实体对于另一些实体有很强的依赖关系，即一个实体的存在必须以另一实体的存在为前提。如果题干改成“患者家属”，答案则是弱实体。</span></span><span style=\"font-family: 宋体; font-size: 10.5pt;\"></span></p><p class=\"MsoNormal\" style=\"text-indent: 20.7pt;\"><span style=\"font-family: 黑体; font-size: 10.5pt; background: #7F7F7F;\"><span style=\"font-family:黑体\">参考答案</span></span><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">：</span></span><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:Calibri\">A</span></span></p>","multi":0,"questionType":1,"answer":"A","chooseItem":["794931049418215425"],"itemList":[{"id":"794931049418215425","questionId":"794931047551750145","content":"实体","answer":1,"chooseValue":"A"},{"id":"794931049443381249","questionId":"794931047551750145","content":"属性","answer":0,"chooseValue":"B"},{"id":"794931049472741377","questionId":"794931047551750145","content":"联系","answer":0,"chooseValue":"C"},{"id":"794931049493712897","questionId":"794931047551750145","content":"弱实体","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931056242348033","title":"<p><span style=\"font-family:宋体\">若给定的关系模式为</span><span style=\"font-family: 宋体; font-size: 10.5pt;\">R</span><span style=\"font-family:宋体\">，</span><span style=\"font-family:Calibri\">U={A,B,C}</span><span style=\"font-family:宋体\">，</span><span style=\"font-family:Calibri\">F = {AB</span><span style=\"font-family:宋体\">→</span><span style=\"font-family:Calibri\">C,C</span><span style=\"font-family:宋体\">→</span><span style=\"font-family:Calibri\">B}</span><span style=\"font-family:宋体\">，则关系</span><span style=\"font-family:Calibri\">R</span><span style=\"font-family:宋体\">（</span><span style=\"font-family:Calibri\"> </span><span style=\"font-family:宋体\">）。</span></p><p class=\"MsoNormal\"><br/></p>","analyze":"<p><br/></p><p class=\"MsoNormal\"><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">将本题关系模式</span>R<span style=\"font-family:宋体\">的函数依赖关系表达为：</span></span><span style=\"font-family: 宋体; font-size: 10.5pt;\">C<span style=\"font-family:宋体\">依赖于</span><span style=\"font-family:Calibri\">A</span><span style=\"font-family:宋体\">和</span><span style=\"font-family:Calibri\">B</span><span style=\"font-family:宋体\">，</span><span style=\"font-family:Calibri\">B</span><span style=\"font-family:宋体\">依赖于</span><span style=\"font-family:Calibri\">C</span><span style=\"font-family:宋体\">。</span></span><span style=\"font-family: Calibri; font-size: 10.5pt;\"></span></p><p class=\"MsoNormal\"><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">因此</span></span><span style=\"font-family: 宋体; font-size: 10.5pt;\">A<span style=\"font-family:宋体\">的入度为零，所以他必然为候选关键字的一部分。</span></span><span style=\"font-family: Calibri; font-size: 10.5pt;\"></span></p><p class=\"MsoNormal\"><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">通过</span>A<span style=\"font-family:宋体\">与</span><span style=\"font-family:Calibri\">B</span><span style=\"font-family:宋体\">组合，或</span><span style=\"font-family:Calibri\">A</span><span style=\"font-family:宋体\">与</span><span style=\"font-family:Calibri\">C</span><span style=\"font-family:宋体\">组合，均能遍历全图，所以候选关系字有：</span><span style=\"font-family:Calibri\">AB</span><span style=\"font-family:宋体\">和</span><span style=\"font-family:Calibri\">AC</span><span style=\"font-family:宋体\">，因此</span><span style=\"font-family:Calibri\">A</span><span style=\"font-family:宋体\">、</span><span style=\"font-family:Calibri\">B</span><span style=\"font-family:宋体\">、</span><span style=\"font-family:Calibri\">C</span><span style=\"font-family:宋体\">均是主属性。</span></span><span style=\"font-family: Calibri; font-size: 10.5pt;\"></span></p><p class=\"MsoNormal\" style=\"text-indent: 20.7pt;\"><span style=\"font-family: 黑体; font-size: 10.5pt; background: #7F7F7F;\"><span style=\"font-family:黑体\">参考答案</span></span><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">：</span></span><span style=\"font-family: 宋体; font-size: 10.5pt;\">B</span></p>","multi":0,"questionType":1,"answer":"B","chooseItem":["794931058138173441"],"itemList":[{"id":"794931058121396225","questionId":"794931056242348033","content":"有2个候选关键字AC和BC，并且有3个主属性","answer":0,"chooseValue":"A"},{"id":"794931058138173441","questionId":"794931056242348033","content":"有2个候选关键字AC和AB，并且有3个主属性","answer":1,"chooseValue":"B"},{"id":"794931058159144961","questionId":"794931056242348033","content":"只有一个候选关键字AC，并且有1个非主属性和2个主属性","answer":0,"chooseValue":"C"},{"id":"794931058175922177","questionId":"794931056242348033","content":"只有一个候选关键字AB，并且有1个非主属性和2个主属性","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931023040237569","title":"<p><br/></p><p class=\"MsoNormal\"><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">关系</span>R、S如下表所示，R÷（πA1</span><span style=\"font-family: 宋体; font-size: 10.5pt;\">,</span><span style=\"font-family: 宋体; font-size: 10.5pt;\">A2(σ 1<3(S)))的结果为</span><span style=\"text-decoration:underline;\"><span style=\"font-family: 宋体; font-size: 10.5pt;\">(44)</span></span><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">。</span></span></p><p class=\"MsoNormal\"><img style=\"max-width:100%;height:auto\" src=\"https://image.chaiding.com/ruankao/1ca60e5cc977a3b8be7a8ee242985dae.png?x-oss-process=style/ruankaodaren\" title=\"1ca60e5cc977a3b8be7a8ee242985dae.png\" alt=\"image.png\"/></p>","analyze":"<p><br/></p><p class=\"MsoNormal\" style=\"text-indent: 21pt; line-height: 150%;\"><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"><span style=\"font-family:宋体\">关系代数的除法运算是同时从关系的水平方向和垂直方向进行运算的。若给定关系</span>R(X，Y)和S(Y，Z)，X、Y、Z属性组，R÷S应当满足元组在X上的分量值x的象集Yx包含S在Y上投影的集合。记作：</span><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"></span></p><p class=\"MsoNormal\" style=\"text-indent: 21pt; line-height: 150%;\"><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"><img style=\"max-width:100%;height:auto\" src=\"https://image.chaiding.com/ruankao/f9d89cfa4dcd574537cabaf6019ada26.png?x-oss-process=style/ruankaodaren\"/></span></p><p class=\"MsoNormal\" style=\"text-indent: 21pt; line-height: 150%;\"><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"><span style=\"font-family:宋体\">其中：</span><span style=\"font-size: 10.5pt; text-indent: 21pt;\">Yx为x在R象集，x=tr[X]。且R÷S的结果集的属性组为X。</span><br/></span></p><p class=\"MsoNormal\" style=\"line-height: 150%;\"><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"><span style=\"font-family:宋体\">根据除法定义，</span>X属性为A3，Y属性为(A1,A2)，R÷S应当满足元组在X上的分量值x的象集Yx包含S在Y上投影的集合，所以结果集的属性为A3。属性A3可以取3个值{3，4，7}，其中：3的象集为{(1，2)}，4的象集为{(2，1)，(3，4)}，7的象集为{(4，6)}。</span><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"></span></p><p class=\"MsoNormal\" style=\"text-indent: 21pt; line-height: 150%;\"><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"><span style=\"font-family:宋体\">根据除法定义，本题关系</span>S为（πA1A2(σ 1<3(S))，在属性组Y(A1A2)上的投影为{(2，1)，(3，4)}如下表所示:</span><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"></span></p><p class=\"MsoNormal\" style=\"line-height: 150%;\"><img style=\"max-width:100%;height:auto\" width=\"287\" height=\"65\" src=\"https://image.chaiding.com/ruankao/c980f523f7be893c505acdd9a4bcb57a.gif?x-oss-process=style/ruankaodaren\"/><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"></span></p><p class=\"MsoNormal\" style=\"text-indent: 21pt; line-height: 150%;\"><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"><span style=\"font-family:宋体\">从以上分析可以看出，只有关系</span>R的属性A3的值为4时，其象集包含了关系S在属性组X即(A1,A2)上的投影，所以R÷S={4}。</span><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"></span></p><p class=\"MsoNormal\" style=\"text-indent: 21pt; line-height: 150%;\"><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\">(45)两个关系R和S进行自然连接时，选择两个关系R和S公共属性上相等的元组，去掉重复的属性列构成新关系。在这种情况下，关系R中的某些元组有可能在关系S中不存在公共属性值上相等的元组，造成关系R中这些元组的值在运算时舍弃了；同样关系S中的某些元组也可能舍弃。为此，扩充了关系运算左外联接、右外联接和完全外联接。</span><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"></span></p><p class=\"MsoNormal\" style=\"line-height: 150%;\"><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"><span style=\"font-family:宋体\">左外联接是指</span>R与S进行自然连接时，只把A中舍弃的元组放到新关系中。</span><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"></span></p><p class=\"MsoNormal\" style=\"line-height: 150%;\"><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"><span style=\"font-family:宋体\">右外联接是指</span>R与S进行自然连接时，只把S中舍弃的元组放到新关系中。</span><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"></span></p><p class=\"MsoNormal\" style=\"line-height: 150%;\"><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"><span style=\"font-family:宋体\">完全外联接是指</span>R与S进行自然连接时，把尺和^中舍弃的元组都放到新关系中。</span><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"></span></p><p class=\"MsoNormal\" style=\"line-height: 150%;\"><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"><span style=\"font-family:宋体\">试题</span>(45)R与S的左外联接、右外联接和完全外联接的结果如下表所示：</span><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"></span></p><p class=\"MsoNormal\" style=\"line-height: 150%;\"><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"><img style=\"max-width:100%;height:auto\" src=\"https://image.chaiding.com/ruankao/eb87bd433a318c284c18e1783992493d.png?x-oss-process=style/ruankaodaren\"/><img style=\"max-width:100%;height:auto\" src=\"https://image.chaiding.com/ruankao/c4f6378bd85e7726f9988f6fade62768.png?x-oss-process=style/ruankaodaren\"/></span></p><p class=\"MsoNormal\" style=\"line-height: 150%;\"><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"><span style=\"font-family:宋体\">从运算的结果可以看出</span><span style=\"font-size: 10.5pt;\">R与S的左外联接、右外联接和完全外联接的元组个数分别为4，4，6。</span><br/></span></p><p class=\"MsoNormal\"><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">参考答案：</span></span><span style=\"font-family: 宋体; font-size: 10.5pt;\">(44)A </span></p>","multi":0,"questionType":1,"answer":"A","chooseItem":["794931024957034497"],"itemList":[{"id":"794931024957034497","questionId":"794931023040237569","content":"{4}","answer":1,"chooseValue":"A"},{"id":"794931024973811713","questionId":"794931023040237569","content":"{3,4}","answer":0,"chooseValue":"B"},{"id":"794931024990588929","questionId":"794931023040237569","content":"{3,4,7}","answer":0,"chooseValue":"C"},{"id":"794931025007366145","questionId":"794931023040237569","content":"{(1,2),(2,1),(3,4),(4,7)}","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931109006692353","title":"在分步设计法中，通常将数据库的设计分为 4 个阶段。其中（请作答此空）是数据库设计的第二阶段，其目标是对需求说明书提供的所有数据和处理要求进行抽象与综合处理建立企业数据模型。（ ）阶段将得到的应用视图转换成外部模式，即特定 DBMS 下的应用视图。","analyze":"数据库概念结构设计是数据库设计的第二阶段，其目标是对需求说明书提供的所有数据和处理要求进行抽象与综合处理，按一定的方法构造反映用户环境的数据及其相互联系的概念模型，即用户的数据模型或企业数据模型。逻辑结构设计的设计目标是把上一阶段得到的与 DBMS 无关的概念数据模型转换成等价的，并为某个特定的 DBMS 所接受的逻辑模型所表示的概念模式，同时将概念设计阶段得到的应用视图转换成外部模式，即特定 DBMS 下的应用视图。","multi":0,"questionType":1,"answer":"B","chooseItem":["794931110885740545"],"itemList":[{"id":"794931110868963329","questionId":"794931109006692353","content":"系统结构设计","answer":0,"chooseValue":"A"},{"id":"794931110885740545","questionId":"794931109006692353","content":"概念结构设计","answer":1,"chooseValue":"B"},{"id":"794931110902517761","questionId":"794931109006692353","content":"逻辑结构设计","answer":0,"chooseValue":"C"},{"id":"794931110915100673","questionId":"794931109006692353","content":"需求概念设计","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931053256003585","title":"<p><br/></p><p class=\"MsoNormal\"><span style=\"font-family: 宋体; font-size: 10.5pt;\"> </span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:Calibri;mso-hansi-font-family:Calibri;mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">关系规范化在数据库设计的（ </span><span style=\"font-family:宋体\">）阶段进行。</span></span></p><p class=\"MsoNormal\" style=\"text-indent:20.7000pt;\"><br/></p>","analyze":"<p><br/></p><p class=\"MsoNormal\" style=\"text-indent: 20.7pt;\"><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">数据库设计中规范化是在逻辑设计阶段进行的一项工作，该工作负责把关系模式进行规范，以减少冗余，以及一定程度上消除修改异常，插入异常及删除异常。</span></span><span style=\"font-family: Calibri; font-size: 10.5pt;\"></span></p><p class=\"MsoNormal\" style=\"text-indent: 20.7pt;\"><span style=\"font-family: 黑体; font-size: 10.5pt; background: #7F7F7F;\"><span style=\"font-family:黑体\">参考答案</span></span><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">：</span></span><span style=\"font-family: 宋体; font-size: 10.5pt;\">C</span></p>","multi":0,"questionType":1,"answer":"C","chooseItem":["794931055286046721"],"itemList":[{"id":"794931055181189121","questionId":"794931053256003585","content":"需求分析","answer":0,"chooseValue":"A"},{"id":"794931055244103681","questionId":"794931053256003585","content":"概念设计","answer":0,"chooseValue":"B"},{"id":"794931055286046721","questionId":"794931053256003585","content":"逻辑设计","answer":1,"chooseValue":"C"},{"id":"794931055327989761","questionId":"794931053256003585","content":"物理设计","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931123137302529","title":"分布透明性指用户不必关心数据的逻辑分片，不必关心数据存储的物理位置分配细节，也不必关心局部场地上数据库的数据模型。（请作答此空）是分布透明性的最高层次。（ ）指用户或应用程序应当了解分片情况，但不必了解片段的存储场地。（ ）透明性是指用户或应用程序应当了解分片及各片断存储的场地，但不必了解局部场地上使用的是何种数据模型。","analyze":"<p>分布透明性包括：分片透明性、位置透明性和局部数据模型透明性。</p><p> （1）分片透明性是分布透明性的最高层次。所谓分片透明性是指用户或应用程序只对全局关系进行操作而不必考虑数据的分片。当分片模式改变时，只要改变全局模式到分片模式的映像（映像 2），而不影响全局模式和应用程序。全局模式不变，应用程序不必改写，这就是分片透明性。</p><p> （2）位置透明性是分布透明性的下一层次。所谓位置透明性是指，用户或应用程序应当了解分片情况，但不必了解片段的存储场地。当存储场地改变时，只要改变分片模式到分配模式的映像（映像 3），而不影响应用程序。同时，若片段的重复副本数目改变了，那么数据的冗余也会改变，但用户不必关心如何保持各副本的一致性，这也提供了重复副本的透明性。</p><p> （3）局部数据模型（逻辑透明）透明性是指用户或应用程序应当了解分片及各片断存储的场地，但不必了解局部场地上使用的是何种数据模型。</p>","multi":0,"questionType":1,"answer":"A","chooseItem":["794931124978601985"],"itemList":[{"id":"794931124978601985","questionId":"794931123137302529","content":"分片透明性","answer":1,"chooseValue":"A"},{"id":"794931124999573505","questionId":"794931123137302529","content":"逻辑透明性","answer":0,"chooseValue":"B"},{"id":"794931125016350721","questionId":"794931123137302529","content":"位置透明性","answer":0,"chooseValue":"C"},{"id":"794931125033127937","questionId":"794931123137302529","content":"全局透明性","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931114648031233","title":"设有职务工资关系P(职务，最低工资，最高工资)，员工关系EMP(员工号，职务，工资)，要求任何一名员工，其工资值必须在其职务对应的工资范围之内，实现该需求的方法是（ ）。","analyze":"完整性约束分为实体完整性约束、参照完整性约束和用户自定义完整性约束三类。其中实体完整性约束可以通过 Primary Key指定，参照完整性约束通过Foreign Key指定，某些简单的约束可以通过Check、Assertion等实现。针对复杂的约束，系统提供了触发器机制，通过用户编程实现。本题中的约束条件只能通过编写职工表上的触发器，在对工资进行修改或插入新记录时触发，将新工资值与工资范围表中职工职务对应的工资范围比对，只有在范围内才提交，否则回滚。","multi":0,"questionType":1,"answer":"C","chooseItem":["794931116531273729"],"itemList":[{"id":"794931116493524993","questionId":"794931114648031233","content":"建立“EMP.职务”向“P.职务”的参照完整性约束","answer":0,"chooseValue":"A"},{"id":"794931116510302209","questionId":"794931114648031233","content":"建立“P.职务”向“EMP.职务”的参照完整性约束","answer":0,"chooseValue":"B"},{"id":"794931116531273729","questionId":"794931114648031233","content":"建立EMP上的触发器程序审定该需求","answer":1,"chooseValue":"C"},{"id":"794931116552245249","questionId":"794931114648031233","content":"建立P上的触发器程序审定该需求","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931222240317441","title":"某磁盘的转速为7200 转/分，传输速度为 4MEB/s，控制器开销为 1ms。要保证读或写一个512字节的扇区的平均时间为11.3ms。那么，该磁盘的平均寻道时间最大应不超过（ ）ms。","analyze":"<p>磁盘读或写一个512字节的扇区所需平均时间应为该磁盘的平均寻道时间+平均旋转时间＋读或写数据的传输时间＋控制器的开销。现在，已知磁盘读或写一个512 字节的扇区所需平均时间=11.3ms 控制器的开销为1ms</p><p>平均旋转时间=0.5×60000÷7200=4.2ms</p><p>读或写数据的传输时间=（1000ms×0.5）÷（4×1024）=0.1ms 从而算出磁盘的平均寻道时间应不超过6.1ms。</p>","multi":0,"questionType":1,"answer":"D","chooseItem":["794931224131948545"],"itemList":[{"id":"794931224081616897","questionId":"794931222240317441","content":"3.9","answer":0,"chooseValue":"A"},{"id":"794931224098394113","questionId":"794931222240317441","content":"4.7","answer":0,"chooseValue":"B"},{"id":"794931224115171329","questionId":"794931222240317441","content":"5.5","answer":0,"chooseValue":"C"},{"id":"794931224131948545","questionId":"794931222240317441","content":"6.1","answer":1,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931188266455041","title":"数据的物理独立性是指当数据库的（22）。","analyze":"<p>数据的逻辑独立性是指当模式改变时（例如增加新的关系，新的属性，改变属性的数据类型等），由数据库管理员对各个外模式/模式的映像做相应的改变，可以使外模式保持不变。应用程序是依据数据的外模式编写的，从而应用程序不必修改，保证了数据与程序的逻辑独立性，简称数据的逻辑独立性。</p><p>数据的物理独立性是指当数据库的存储结构改变了，由数据库管理员对模式/内模式映像做响应的改变，可以使模式保持不变，从而应用程序也不必改变，保证了数据与程序的物理独立性，简称数据的物理独立性。</p>","multi":0,"questionType":1,"answer":"B","chooseItem":["794931190141308929"],"itemList":[{"id":"794931190124531713","questionId":"794931188266455041","content":"外模式发生改变时，数据的物理结构需要改变","answer":0,"chooseValue":"A"},{"id":"794931190141308929","questionId":"794931188266455041","content":"内模式发生改变时，数据的逻辑结构不需要改变","answer":1,"chooseValue":"B"},{"id":"794931190162280449","questionId":"794931188266455041","content":"外模式发生改变时，数据的逻辑结构不需要改变","answer":0,"chooseValue":"C"},{"id":"794931190179057665","questionId":"794931188266455041","content":"内模式发生改变时，数据的物理结构不需要改变","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931111846236161","title":"<p>在分步设计法中，通常将数据库的设计分为 4 个阶段。其中（ ）是数据库设计的第二阶段，其目标是对需求说明书提供的所有数据和处理要求进行抽象与综合处理建立企业数据模型。（请作答此空）阶段将得到的应用视图转换成外部模式，即特定 DBMS 下的应用视图。</p>","analyze":"<p>数据库概念结构设计是数据库设计的第二阶段，其目标是对需求说明书提供的所有数据和处理要求进行抽象与综合处理，按一定的方法构造反映用户环境的数据及其相互联系的概念模型，即用户的数据模型或企业数据模型。逻辑结构设计的设计目标是把上一阶段得到的与 DBMS 无关的概念数据模型转换成等价的，并为某个特定的 DBMS 所接受的逻辑模型所表示的概念模式，同时将概念设计阶段得到的应用视图转换成外部模式，即特定 DBMS 下的应用视图。</p>","multi":0,"questionType":1,"answer":"B","chooseItem":["794931113708507137"],"itemList":[{"id":"794931113695924225","questionId":"794931111846236161","content":"系统结构设计","answer":0,"chooseValue":"A"},{"id":"794931113708507137","questionId":"794931111846236161","content":"概念结构设计","answer":1,"chooseValue":"B"},{"id":"794931113721090049","questionId":"794931111846236161","content":"逻辑结构设计","answer":0,"chooseValue":"C"},{"id":"794931113742061569","questionId":"794931111846236161","content":"物理结构设计","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931262270754817","title":"<p>某高校信息系统釆用分布式数据库系统，该系统中“每结点对本地数据都能独立管理”和“数据在不同场地上的存储”分别称为分布式数据库的 （20） 。</p>","analyze":"<p>共享性是指各结点数据共享；自治性指每结点对本地数据都能独立管理；可用性是指当某一场地故障时，系统可以使用其他场地上的副本而不至于使整个系统瘫痪；分布性是指数据在不同场地上的存储。</p>","multi":0,"questionType":1,"answer":"B","chooseItem":["794931264263049217"],"itemList":[{"id":"794931264246272001","questionId":"794931262270754817","content":"共享性和分布性","answer":0,"chooseValue":"A"},{"id":"794931264263049217","questionId":"794931262270754817","content":"自治性和分布性","answer":1,"chooseValue":"B"},{"id":"794931264279826433","questionId":"794931262270754817","content":"自治性和可用性","answer":0,"chooseValue":"C"},{"id":"794931264292409345","questionId":"794931262270754817","content":"可用性和分布性","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931219421745153","title":"<p>（ ）是一种信息分析工具，能自动地找出数据仓库中的模式及关系。</p>","analyze":"<p>数据仓库是一个数据库，它存储的信息来源于企业的多个数据源，为业务用户提供了分析组织业务状态所需数据的多维视图，专为支持管理决策而设计。一般而言，数据仓库是非常庞大的数据库，包含了数以百万甚至千万计的数据记录。</p><p>数据集是数据仓库的一个子集，满足组织中的业务部门从事务处理系统收集来的业务数据进行联机分析的需要。数据集并不在单一的数据库中存放企业所有的数据，而是仅包含了公司业务某一方面的数据子集（如财务等），其为某特定领域提供的数据可能比数据仓库提供的更详细。</p><p>数据挖掘是一种信息分析工具，利用先进的统计技术及机器学习技术。在大型的数据库中发现事实。数据挖掘能够自动地找到数据仓库中的模式及关系，是决策支持解决方案的下一步发展趋势。</p><p>预测分析将历史数据与关于未来的假设结合起来，预测事件的结果。</p><p></p>","multi":0,"questionType":1,"answer":"B","chooseItem":["794931221292404737"],"itemList":[{"id":"794931221275627521","questionId":"794931219421745153","content":"数据集市","answer":0,"chooseValue":"A"},{"id":"794931221292404737","questionId":"794931219421745153","content":"数据挖掘","answer":1,"chooseValue":"B"},{"id":"794931221313376257","questionId":"794931219421745153","content":"预测分析","answer":0,"chooseValue":"C"},{"id":"794931221334347777","questionId":"794931219421745153","content":"数据统计","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931289047191553","title":"<p>在数据库的安全机制中，通过提供 （19） 供开发人员调用进行数据查询，从而保证保密的数据对无权限的用户隐藏。</p>","analyze":"<p>通过为用户定义视图（VIEW）把数据对用户的呈现限定在一定的范围内，把要保密的数据对无权限的用户隐藏，从而提供一定程度的安全保护。</p><p>参考答案：B</p>","multi":0,"questionType":1,"answer":"B","chooseItem":["794931290934628353"],"itemList":[{"id":"794931290917851137","questionId":"794931289047191553","content":"索引","answer":0,"chooseValue":"A"},{"id":"794931290934628353","questionId":"794931289047191553","content":"视图","answer":1,"chooseValue":"B"},{"id":"794931290955599873","questionId":"794931289047191553","content":"触发器","answer":0,"chooseValue":"C"},{"id":"794931290976571393","questionId":"794931289047191553","content":"存储过程","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931125972652033","title":"分布透明性指用户不必关心数据的逻辑分片，不必关心数据存储的物理位置分配细节，也不必关心局部场地上数据库的数据模型。（ ）是分布透明性的最高层次。（请作答此空）指用户或应用程序应当了解分片情况，但不必了解片段的存储场地。（ ）透明性是指用户或应用程序应当了解分片及各片断存储的场地，但不必了解局部场地上使用的是何种数据模型。","analyze":"<p>分布透明性包括：分片透明性、位置透明性和局部数据模型透明性。</p><p> （1）分片透明性是分布透明性的最高层次。所谓分片透明性是指用户或应用程序只对全局关系进行操作而不必考虑数据的分片。当分片模式改变时，只要改变全局模式到分片模式的映像（映像 2），而不影响全局模式和应用程序。全局模式不变，应用程序不必改写，这就是分片透明性。</p><p> （2）位置透明性是分布透明性的下一层次。所谓位置透明性是指，用户或应用程序应当了解分片情况，但不必了解片段的存储场地。当存储场地改变时，只要改变分片模式到分配模式的映像（映像 3），而不影响应用程序。同时，若片段的重复副本数目改变了，那么数据的冗余也会改变，但用户不必关心如何保持各副本的一致性，这也提供了重复副本的透明性。</p><p> （3）局部数据模型（逻辑透明）透明性是指用户或应用程序应当了解分片及各片断存储的场地，但不必了解局部场地上使用的是何种数据模型。</p>","multi":0,"questionType":1,"answer":"C","chooseItem":["794931127881060353"],"itemList":[{"id":"794931127843311617","questionId":"794931125972652033","content":"分片透明性","answer":0,"chooseValue":"A"},{"id":"794931127860088833","questionId":"794931125972652033","content":"逻辑透明性","answer":0,"chooseValue":"B"},{"id":"794931127881060353","questionId":"794931125972652033","content":"位置透明性","answer":1,"chooseValue":"C"},{"id":"794931127897837569","questionId":"794931125972652033","content":"全局透明性","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931117466603521","title":" 设关系模式R(U，F)，其中R上的属性集U={A，B，C，D，E}，R上的函数依赖集 F={A→B,DE→B，CB→E，E→A，B→D}。 （请作答此空）为关系R的候选关键字。分解（ ）是无损连接，并保持函数依赖的。","analyze":"<p><img style=\"max-width:100%;height:auto\" src=\"https://image.chaiding.com/ruankao/99b6a3bae7957010561a0f03c9b984d8.jpg?x-oss-process=style/ruankaodaren\" title=\"99b6a3bae7957010561a0f03c9b984d8.jpg\" alt=\"1.jpg\"/>根据无损连接的判定算法，对选项A构造初始的判定表如下：<br/><img style=\"max-width:100%;height:auto\" src=\"https://image.chaiding.com/ruankao/0aeacb4ee7e1451ec260ecaa52788949.jpg?x-oss-process=style/ruankaodaren\" title=\"0aeacb4ee7e1451ec260ecaa52788949.jpg\" alt=\"1.jpg\"/></p><p>由于A→B，DE→B，CB→E，E→A，B→D的决定因素中没有两行是相同的，因此选项 A是有损连接的。 对选项B构造初始的判定表如下：</p><p><img style=\"max-width:100%;height:auto\" src=\"https://image.chaiding.com/ruankao/64def8c41297735e5b2f8e66b9d4d277.jpg?x-oss-process=style/ruankaodaren\" title=\"64def8c41297735e5b2f8e66b9d4d277.jpg\" alt=\"1.jpg\"/><img style=\"max-width:100%;height:auto\" src=\"https://image.chaiding.com/ruankao/e17ea53e710e972928d10336615e6952.jpg?x-oss-process=style/ruankaodaren\" title=\"e17ea53e710e972928d10336615e6952.jpg\" alt=\"1.jpg\"/></p><p>由于A→B,DE→B,CB→E，E→A，B→D的决定因素中没有两行是相同的，因此选项 B是有损连接的。 对选项C构造初始的判定表如下：</p><p><img style=\"max-width:100%;height:auto\" src=\"https://image.chaiding.com/ruankao/a6b25fd202109600160d89a937b07925.jpg?x-oss-process=style/ruankaodaren\" title=\"a6b25fd202109600160d89a937b07925.jpg\" alt=\"1.jpg\"/></p><p>由于A→B，属性A的第1行和第3行相同，可以将第1行b12改为a2；又由于B→D，属性B的第1行和第3行相同，而属性D第1行b14和第3行b34没有一行为a4，因此改为同一符号，即取行号值最小的b14。修改后的判定表如下：<br/><img style=\"max-width:100%;height:auto\" src=\"https://image.chaiding.com/ruankao/2911caa110378443ba8a5d90b9650a33.jpg?x-oss-process=style/ruankaodaren\" title=\"2911caa110378443ba8a5d90b9650a33.jpg\" alt=\"1.jpg\"/></p><p>反复检查函数依赖集F，无法修改上表，所以选项C是有损连接的。 对选项D构造初始的判定表如下：<br/><img style=\"max-width:100%;height:auto\" src=\"https://image.chaiding.com/ruankao/da51d2c9f5d121a67651ca13a9ac788f.jpg?x-oss-process=style/ruankaodaren\" title=\"da51d2c9f5d121a67651ca13a9ac788f.jpg\" alt=\"1.jpg\"/></p><p>由于A→B，属性A的第1行和第3行相同，可以将第3行b32改为a2；E→A，属性E的第2行和第3行相同，可以将属性A第2行b21改为a1；AC→E，属性E的第2行和第3行相同，可以将属性E第1行b15改为a5；B→D，属性B的第1行和第3行相同，属性D第1行b14和第3行b34没有一行为a4，因此改为同一符号，即取行号值最小的b14。修改后的判定表如下：<br/><img style=\"max-width:100%;height:auto\" src=\"https://image.chaiding.com/ruankao/b08bd1aa719dce5bc11e24eeb3933382.jpg?x-oss-process=style/ruankaodaren\" title=\"b08bd1aa719dce5bc11e24eeb3933382.jpg\" alt=\"1.jpg\"/></p><p>由于E→D，属性E的第1～3行相同，可以将属性D第1行b14和第3行b34改为a4。修改后的判定表如下：<br/><img style=\"max-width:100%;height:auto\" src=\"https://image.chaiding.com/ruankao/cb47fc7b54890cee225292e37773b3a6.jpg?x-oss-process=style/ruankaodaren\" title=\"cb47fc7b54890cee225292e37773b3a6.jpg\" alt=\"1.jpg\"/></p><p>由于上表第一行全为a，故分解无损。</p><p>现在分析该分解是否保持函数依赖。若分解保持函数依赖，那么分解的子模式的函数依赖集<img style=\"max-width:100%;height:auto\" src=\"https://image.chaiding.com/ruankao/717a7f9b9b320da0949ec078d4b66064.jpg?x-oss-process=style/ruankaodaren\" title=\"717a7f9b9b320da0949ec078d4b66064.jpg\" alt=\"1.jpg\"/>。FR1=A→B,CB→A，FR2=E→D(根据Armstrong公理，系统传递依赖，E→A，A→B，B→D，所以E→D)，FR3=E→A。可以求证F+与(FR1+FR2+FR3)+等价，即F+=(FR1+FR2+FR3)+=(A→B,CB→A,E→D,E→A)+，所以该分解保持函数依赖。</p>","multi":0,"questionType":1,"answer":"C","chooseItem":["794931119375011841"],"itemList":[{"id":"794931119333068801","questionId":"794931117466603521","content":"AB","answer":0,"chooseValue":"A"},{"id":"794931119358234625","questionId":"794931117466603521","content":"DE","answer":0,"chooseValue":"B"},{"id":"794931119375011841","questionId":"794931117466603521","content":"CE","answer":1,"chooseValue":"C"},{"id":"794931119391789057","questionId":"794931117466603521","content":"DB","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931233497829377","title":"<p>数据仓库中的（）消除了源数据中的不一致性，提供整个企业的一致性全局信息。</p>","analyze":"<p>数据仓库4大特点：</p><p>面向主题：数据按主题组织。</p><p>集成的：消除了源数据中的不一致性，提供整个企业的一致性全局信息。</p><p>相对稳定的(非易失的)：主要进行查询操作，只有少量的修改和删除操作（或是不删除）。</p><p>反映历史变化(随着时间变化)：记录了企业从过去某一时刻到当前各个阶段的信息，可对发展历程和未来趋势做定量分析和预测。</p>","multi":0,"questionType":1,"answer":"B","chooseItem":["794931235360100353"],"itemList":[{"id":"794931235343323137","questionId":"794931233497829377","content":"面向主题性","answer":0,"chooseValue":"A"},{"id":"794931235360100353","questionId":"794931233497829377","content":"集成性","answer":1,"chooseValue":"B"},{"id":"794931235376877569","questionId":"794931233497829377","content":"稳定性","answer":0,"chooseValue":"C"},{"id":"794931235393654785","questionId":"794931233497829377","content":"反映历史变化性","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931225042112513","title":"<p>在五级流水线的嵌入式处理器设计中，一般包括取指、译码、执行、访存和回写。下面对这五个阶段描述不正确的是（ ）</p>","analyze":"<p>在典型的五级流水线的嵌入式处理器设计中（如 ARM9），其过程包括取指、译码、执行、访存和回写五个步骤。其中取指是指从存储器中取出指令，并将其放入指令流水线；译码是指对指令进行译码解码；执行是指利用逻辑运算单元进行运算的执行；访存是指在需要情况下进行数据存储器的访问；回写是指将指令产生的结果回写到寄存器中，包括任何从存储器中读取的数据。</p>","multi":0,"questionType":1,"answer":"D","chooseItem":["794931226954715137"],"itemList":[{"id":"794931226891800577","questionId":"794931225042112513","content":"取指是指从存储器中取出指令，并将其放入指令流水线","answer":0,"chooseValue":"A"},{"id":"794931226912772097","questionId":"794931225042112513","content":"译码是指对指令进行译码，执行是指通过算术逻辑单元进行运算","answer":0,"chooseValue":"B"},{"id":"794931226933743617","questionId":"794931225042112513","content":"访存是指访问数据存储器","answer":0,"chooseValue":"C"},{"id":"794931226954715137","questionId":"794931225042112513","content":"回写是指将指令产生的结果回写到外部存储器","answer":1,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931061934018561","title":"<p><br/></p><p class=\"MsoNormal\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:Calibri;mso-hansi-font-family:Calibri;mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">某公司数据库中的元件关系模式为</span>P<span style=\"font-family:宋体\">（元件号，元件名称，供应商，供应商所在地，库存量），函数依赖集</span><span style=\"font-family:Calibri\">F</span><span style=\"font-family:宋体\">如下所示：</span></span><span style=\"mso-spacerun:'yes';font-family:Calibri;mso-fareast-font-family:宋体;mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p><p class=\"MsoNormal\" style=\"margin-left:0.0000pt;mso-para-margin-left:0.0000gd;text-indent:0.0000pt;mso-char-indent-count:0.0000;\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:Calibri;mso-hansi-font-family:Calibri;mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"> F={<span style=\"font-family:宋体\">元件号→元件名称，（元件号，供应商）→库存量，供应商→供应商所在地</span><span style=\"font-family:Calibri\">}</span></span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:Calibri;mso-hansi-font-family:Calibri;mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">，</span></span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:Calibri;mso-hansi-font-family:Calibri;mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">元件关系的主键为</span></span><span style=\"font-family: 宋体; font-size: 10.5pt;\">元件号，供应商</span><span style=\"font-family: 宋体; font-size: 10.5pt; text-indent: 0pt;\">，该关系存在冗余以及插入异常和删除异常等问题。</span><span style=\"font-family:宋体;font-family: 宋体; font-size: 10.5pt;\">为了解决这一问题需要将元件关系分解（ </span><span style=\"font-family:宋体;font-family: 宋体; font-size: 10.5pt;\">）</span></p><p class=\"MsoNormal\"><br/></p>","analyze":"<p><br/></p><p>因为关系模式P存在冗余以及插入异常和删除异常等问题。<br/></p>为了解决这一问题需要将元件关系分解。选项A，选项B和选项D是有损连接的，且不保持函数依赖性故分解是错误的，例如，分解为选项A、选项B和选项D后，用户无法查询某元件由哪些供应商供应，原因是分解有损连接的，且不保持函数依赖。<p><br/></p>","multi":0,"questionType":1,"answer":"C","chooseItem":["794931063884369921"],"itemList":[{"id":"794931063813066753","questionId":"794931061934018561","content":"元件1（元件号，元件名称，库存量）、元件2（供应商，供应商所在地）","answer":0,"chooseValue":"A"},{"id":"794931063842426881","questionId":"794931061934018561","content":"元件1（元件号，元件名称）、元件2（供应商，供应商所在地，库存量）","answer":0,"chooseValue":"B"},{"id":"794931063884369921","questionId":"794931061934018561","content":"元件1（元件号，元件名称）、元件2（元件号，供应商，库存量）、元件3（供应商，供应商所在地）","answer":1,"chooseValue":"C"},{"id":"794931063909535745","questionId":"794931061934018561","content":"元件1（元件号，元件名称）、元件2（元件号，库存量）、元件3（供应商，供应商所在地）、元件4（供应商所在地，库存量）","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931286216036353","title":"在多用户共享系统中，许多事务可能同时对同一数据进行操作，由DBMS的 (17)子系统负责保证数据库的完整性不受破坏。","analyze":"<p>在多用户共享系统中，许多事务可能同时对同一数据进行操作，称为并发操作。此时，由DBMS的并发控制子系统负责协调并发事务的执行，保证数据库的完整性不受破坏，同时，避免用户得到不正确的数据。</p><p>参考答案：D</p><p><br/></p>","multi":0,"questionType":1,"answer":"D","chooseItem":["794931288111861761"],"itemList":[{"id":"794931288057335809","questionId":"794931286216036353","content":"封锁管理","answer":0,"chooseValue":"A"},{"id":"794931288069918721","questionId":"794931286216036353","content":"进程管理","answer":0,"chooseValue":"B"},{"id":"794931288090890241","questionId":"794931286216036353","content":"日志管理","answer":0,"chooseValue":"C"},{"id":"794931288111861761","questionId":"794931286216036353","content":"并发控制 <br/>","answer":1,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931097589796865","title":"<p>给定关系R（A,B,C,D,E）与S（A,B,C,F,G），那么与表达式<img style=\"max-width:100%;height:auto\" src=\"https://image.chaiding.com/ruankao/d94000d6ad02f314f138d8290840fe50.png?x-oss-process=style/ruankaodaren\" title=\"d94000d6ad02f314f138d8290840fe50.png\" alt=\"blob.png\"/>等价的SQL语句如下：select （） from R, S where （作答此空）。</p>","analyze":"<p>本题考查关系代数运算与SQL语言的对应关系，注意本题中R与S是做自然连接操作，操作时会将R与S中相同字段名做等值连接，并将结果集去重复。所以R与S自然连接后的结果包括以下属性：</p><p>R.A，R.B，R.C，D，E，F，G。</p><p>关系代数选择条件为“1<6”，即R.A<F。</p><p>关系代数投影操作条件为“1,2,4,6,7”，对应的属性为R.A，R.B，D，F，G。</p><p><br/></p>","multi":0,"questionType":1,"answer":"C","chooseItem":["794931099481427969"],"itemList":[{"id":"794931099443679233","questionId":"794931097589796865","content":"R.A=S.A OR R.B=S.B OR R.C=S.C OR R.A<S.F","answer":0,"chooseValue":"A"},{"id":"794931099460456449","questionId":"794931097589796865","content":"R.A=S.A OR R.B=S.B OR R.C=S.C OR R.A<S.B","answer":0,"chooseValue":"B"},{"id":"794931099481427969","questionId":"794931097589796865","content":"R.A=S.A AND R.B=S.B AND R.C=S.C AND R.A<S.F","answer":1,"chooseValue":"C"},{"id":"794931099502399489","questionId":"794931097589796865","content":"R.A=S.A AND R.B=S.B AND R.C=S.C AND R.A<S.B","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931265194184705","title":"<p>给定关系模式 R<U,F>;其中 U 为属性集，F 是 U 上的一组函数依赖，那么 Armstroog 公理系统的增广律是指（ ）。</p>","analyze":"<p>Armstrong 公理函数依赖的推理规则有以下三条：</p><p>自反律：若属性集Y 包含于属性集X，属性集X 包含于U，则X→Y 在R 上成立。(此处X→Y是平凡函数依赖)</p><p>增广律：若X→Y 在R 上成立，且属性集Z 包含于属性集U，则XZ→YZ 在R 上成立。</p><p>传递律：若X→Y 和 Y→Z在R 上成立，则X →Z 在R 上成立。</p><p>其他的所有函数依赖的推理规则可以使用这三条规则推导出。</p>","multi":0,"questionType":1,"answer":"D","chooseItem":["794931267220033537"],"itemList":[{"id":"794931267169701889","questionId":"794931265194184705","content":"若 X→Y，X→Z，则 X→YZ 为 F 所蕴涵","answer":0,"chooseValue":"A"},{"id":"794931267186479105","questionId":"794931265194184705","content":"若 X→Y，WY→Z，则 XW→Z 为 F 所蕴涵","answer":0,"chooseValue":"B"},{"id":"794931267203256321","questionId":"794931265194184705","content":"若 X→Y，Y→Z 为 F 所蕴涵，则 X→Z 为 F 所蕴涵","answer":0,"chooseValue":"C"},{"id":"794931267220033537","questionId":"794931265194184705","content":"若X→Y，为F 所蕴涵，且Z⊆U,则入XZ→YZ 为F 所蕴涵","answer":1,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931067709575169","title":"<p><img style=\"max-width:100%;height:auto\" src=\"https://image.chaiding.com/ruankao/36f762e14df168451e5dd1c1708865a2.png?x-oss-process=style/ruankaodaren\"/></p>","analyze":"<p><br/></p><p class=\"MsoNormal\"><span style=\"mso-spacerun:'yes';font-family:宋体;font-size:12.0000pt;mso-font-kerning:0.0000pt;\">本题前一空分析：</span><span style=\"mso-spacerun:'yes';font-family:宋体;font-size:12.0000pt;mso-font-kerning:0.0000pt;\"><br/></span><span style=\"mso-spacerun:'yes';font-family:宋体;font-size:12.0000pt;mso-font-kerning:0.0000pt;\">A选项的关系代数表达式，错误之处在于选择的两个条件不应为“或”关系。</span><span style=\"mso-spacerun:'yes';font-family:宋体;font-size:12.0000pt;mso-font-kerning:0.0000pt;\"><br/></span><span style=\"mso-spacerun:'yes';font-family:宋体;font-size:12.0000pt;mso-font-kerning:0.0000pt;\"> B选项的关系代数表达式，错误之处在于R与S仅做了笛卡尔积的操作，并没有把相同属性列做等值判断。应加上：2=4及3=5的选择条件才对。</span><span style=\"mso-spacerun:'yes';font-family:宋体;font-size:12.0000pt;mso-font-kerning:0.0000pt;\"><br/></span><span style=\"mso-spacerun:'yes';font-family:宋体;font-size:12.0000pt;mso-font-kerning:0.0000pt;\"> C选项的关系代数表达式，与B选项有相同错误，同时投影列号还不正确。</span><span style=\"mso-spacerun:'yes';font-family:宋体;font-size:12.0000pt;mso-font-kerning:0.0000pt;\"><br/></span><span style=\"mso-spacerun:'yes';font-family:宋体;font-size:12.0000pt;mso-font-kerning:0.0000pt;\"> 后面一空，首先值得说明的是，选项中有一个共同的错误，即“S.A4<’95’”应修改为“S.A4=’95’”。</span><span style=\"mso-spacerun:'yes';font-family:宋体;font-size:12.0000pt;mso-font-kerning:0.0000pt;\"><br/></span><span style=\"mso-spacerun:'yes';font-family:宋体;font-size:12.0000pt;mso-font-kerning:0.0000pt;\"> 选项中几个条件都是正确的，需要选择的，其实只是使用AND还是OR来进行连接。由于进行自然连接以及相关条件判断都是同时要成立的，所以必须都要用AND进行连接。</span><span style=\"mso-spacerun:'yes';font-family:Calibri;mso-fareast-font-family:宋体;mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p>","multi":0,"questionType":1,"answer":"D","chooseItem":["794931069638955009"],"itemList":[{"id":"794931069580234753","questionId":"794931067709575169","content":"A","answer":0,"chooseValue":"A"},{"id":"794931069601206273","questionId":"794931067709575169","content":"B","answer":0,"chooseValue":"B"},{"id":"794931069622177793","questionId":"794931067709575169","content":"C","answer":0,"chooseValue":"C"},{"id":"794931069638955009","questionId":"794931067709575169","content":"D","answer":1,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931029105201153","title":"<p><br/></p><p class=\"MsoNormal\"><span style=\"mso-spacerun:'yes';font-family:宋体;font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">在数据库系统中，数据库的视图、基本表和存储文件的结构分别与</span></span><span style=\"text-decoration:underline;\"><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">（</span>40）</span></span><span style=\"mso-spacerun:'yes';font-family:宋体;font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">对应。</span></span></p>","analyze":"<p><br/></p><p class=\"MsoNormal\"><span style=\"mso-spacerun:'yes';font-family:宋体;font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">数据库通常采用三级模式结构，其中，视图对应外模式、基本表对应模式、存储文件对应内模式。</span></span></p><p class=\"MsoNormal\"><span style=\"font-family: 宋体; font-size: 10.5pt; background: #7F7F7F;\"><span style=\"font-family:宋体\">参考答案</span></span><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">：</span></span><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">（</span></span><span style=\"font-family: 宋体; font-size: 10.5pt;\">40）C </span></p>","multi":0,"questionType":1,"answer":"C","chooseItem":["794931031567257601"],"itemList":[{"id":"794931031529508865","questionId":"794931029105201153","content":"模式、外模式、内模式","answer":0,"chooseValue":"A"},{"id":"794931031550480385","questionId":"794931029105201153","content":"模式、内模式、外模式","answer":0,"chooseValue":"B"},{"id":"794931031567257601","questionId":"794931029105201153","content":"外模式、模式、内模式","answer":1,"chooseValue":"C"},{"id":"794931031584034817","questionId":"794931029105201153","content":"外模式、内模式、模式","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931128812195841","title":"<p>分布透明性指用户不必关心数据的逻辑分片，不必关心数据存储的物理位置分配细节，也不必关心局部场地上数据库的数据模型。（ ）是分布透明性的最高层次。（ ）指用户或应用程序应当了解分片情况，但不必了解片段的存储场地。（请作答此空）透明性是指用户或应用程序应当了解分片及各片断存储的场地，但不必了解局部场地上使用的是何种数据模型。</p>","analyze":"<p>分布透明性包括：分片透明性、位置透明性和局部数据模型透明性。</p><p> （1）分片透明性是分布透明性的最高层次。所谓分片透明性是指用户或应用程序只对全局关系进行操作而不必考虑数据的分片。当分片模式改变时，只要改变全局模式到分片模式的映像（映像 2），而不影响全局模式和应用程序。全局模式不变，应用程序不必改写，这就是分片透明性。</p><p> （2）位置透明性是分布透明性的下一层次。所谓位置透明性是指，用户或应用程序应当了解分片情况，但不必了解片段的存储场地。当存储场地改变时，只要改变分片模式到分配模式的映像（映像 3），而不影响应用程序。同时，若片段的重复副本数目改变了，那么数据的冗余也会改变，但用户不必关心如何保持各副本的一致性，这也提供了重复副本的透明性。</p><p> （3）局部数据模型（逻辑透明）透明性是指用户或应用程序应当了解分片及各片断存储的场地，但不必了解局部场地上使用的是何种数据模型。</p>","multi":0,"questionType":1,"answer":"B","chooseItem":["794931130691244033"],"itemList":[{"id":"794931130674466817","questionId":"794931128812195841","content":"分片透明性","answer":0,"chooseValue":"A"},{"id":"794931130691244033","questionId":"794931128812195841","content":"逻辑透明性","answer":1,"chooseValue":"B"},{"id":"794931130708021249","questionId":"794931128812195841","content":"位置透明性","answer":0,"chooseValue":"C"},{"id":"794931130724798465","questionId":"794931128812195841","content":"全局透明性","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931120306147329","title":"设关系模式R(U，F)，其中R上的属性集U={A，B，C，D，E}，R上的函数依赖集 F={A→B,DE→B，CB→E，E→A，B→D}。 （ ）为关系R的候选关键字。分解（请作答此空）是无损连接，并保持函数依赖的。","analyze":"<p><img style=\"max-width:100%;height:auto\" src=\"https://image.chaiding.com/ruankao/48cacefa253fe955bf081e3af3e067c4.jpg?x-oss-process=style/ruankaodaren\" title=\"48cacefa253fe955bf081e3af3e067c4.jpg\" alt=\"1.jpg\"/>根据无损连接的判定算法，对选项A构造初始的判定表如下：<br/><img style=\"max-width:100%;height:auto\" src=\"https://image.chaiding.com/ruankao/0cdeb9b5112459de995effbbdf9958f5.jpg?x-oss-process=style/ruankaodaren\" title=\"0cdeb9b5112459de995effbbdf9958f5.jpg\" alt=\"1.jpg\"/></p><p>由于A→B，DE→B，CB→E，E→A，B→D的决定因素中没有两行是相同的，因此选项 A是有损连接的。 对选项B构造初始的判定表如下： </p><p><img style=\"max-width:100%;height:auto\" src=\"https://image.chaiding.com/ruankao/83d4d2c9a3048643d19108c1dccfc6ac.jpg?x-oss-process=style/ruankaodaren\" title=\"83d4d2c9a3048643d19108c1dccfc6ac.jpg\" alt=\"1.jpg\"/></p><p>由于A→B,DE→B,CB→E，E→A，B→D的决定因素中没有两行是相同的，因此选项 B是有损连接的。 对选项C构造初始的判定表如下： <br/><img style=\"max-width:100%;height:auto\" src=\"https://image.chaiding.com/ruankao/0251b2bf32088cc2c3344d1a66c872c7.jpg?x-oss-process=style/ruankaodaren\" title=\"0251b2bf32088cc2c3344d1a66c872c7.jpg\" alt=\"1.jpg\"/></p><p>由于A→B，属性A的第1行和第3行相同，可以将第1行b12改为a2；又由于B→D，属性B的第1行和第3行相同，而属性D第1行b14和第3行b34没有一行为a4，因此改为同一符号，即取行号值最小的b14。修改后的判定表如下：<br/><img style=\"max-width:100%;height:auto\" src=\"https://image.chaiding.com/ruankao/45b2c2ae8b09515f0407a52c9251ac5d.jpg?x-oss-process=style/ruankaodaren\" title=\"45b2c2ae8b09515f0407a52c9251ac5d.jpg\" alt=\"1.jpg\"/></p><p>反复检查函数依赖集F，无法修改上表，所以选项C是有损连接的。 对选项D构造初始的判定表如下： <br/><img style=\"max-width:100%;height:auto\" src=\"https://image.chaiding.com/ruankao/54bcbd3c45348b384ba1da7e90972f35.jpg?x-oss-process=style/ruankaodaren\" title=\"54bcbd3c45348b384ba1da7e90972f35.jpg\" alt=\"1.jpg\"/></p><p>由于A→B，属性A的第1行和第3行相同，可以将第3行b32改为a2；E→A，属性E的第2行和第3行相同，可以将属性A第2行b21改为a1；AC→E，属性E的第2行和第3行相同，可以将属性E第1行b15改为a5；B→D，属性B的第1行和第3行相同，属性D第1行b14和第3行b34没有一行为a4，因此改为同一符号，即取行号值最小的b14。修改后的判定表如下：<br/><img style=\"max-width:100%;height:auto\" src=\"https://image.chaiding.com/ruankao/b82fcfe474e9b5e7b1001f394fc47598.jpg?x-oss-process=style/ruankaodaren\" title=\"b82fcfe474e9b5e7b1001f394fc47598.jpg\" alt=\"1.jpg\"/></p><p>由于E→D，属性E的第1～3行相同，可以将属性D第1行b14和第3行b34改为a4。修改后的判定表如下：<br/><img style=\"max-width:100%;height:auto\" src=\"https://image.chaiding.com/ruankao/9105158e04a56cb8582bdac236406764.jpg?x-oss-process=style/ruankaodaren\" title=\"9105158e04a56cb8582bdac236406764.jpg\" alt=\"1.jpg\"/></p><p>由于上表第一行全为a，故分解无损。</p><p>现在分析该分解是否保持函数依赖。若分解保持函数依赖，那么分解的子模式的函数依赖集<img style=\"max-width:100%;height:auto\" src=\"https://image.chaiding.com/ruankao/e29c96f7d252667e5f0e1ef291efe46c.jpg?x-oss-process=style/ruankaodaren\" title=\"e29c96f7d252667e5f0e1ef291efe46c.jpg\" alt=\"1.jpg\"/>。FR1=A→B,CB→A，FR2=E→D(根据Armstrong公理，系统传递依赖，E→A，A→B，B→D，所以E→D)，FR3=E→A。可以求证F+与(FR1+FR2+FR3)+等价，即F+=(FR1+FR2+FR3)+=(A→B,CB→A,E→D,E→A)+，所以该分解保持函数依赖</p><p><br/></p>","multi":0,"questionType":1,"answer":"D","chooseItem":["794931122227138561"],"itemList":[{"id":"794931122181001217","questionId":"794931120306147329","content":"ρ={R1(AC)，R2(ED)，R3(B)}","answer":0,"chooseValue":"A"},{"id":"794931122197778433","questionId":"794931120306147329","content":"ρ={R1(AC)，R2(E)，R3(DB)}","answer":0,"chooseValue":"B"},{"id":"794931122210361345","questionId":"794931120306147329","content":"ρ={R1(AC)，R2(ED)，R3(AB)}","answer":0,"chooseValue":"C"},{"id":"794931122227138561","questionId":"794931120306147329","content":"ρ={R1(ABC)，R2(ED)，R3(ACE)}","answer":1,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931253466910721","title":"<p>若事务T1对数据D1已加共享锁，事务T2对数据D2已加排他锁，那么 （17） 。</p>","analyze":"<p>为了保持并发控制中，数据库数据的一致性。引入了排它锁（X锁）和共享锁（S锁）。</p><p>并且，规定：</p><p>（1）事务T对数据A加X锁，则不允许其他事务对数据A加任何类型锁。</p><p>（2）事务T对数据A加S锁，则允许其他事务对数据A加S锁，但不允许加X锁。</p><p>因此，本题事务T1对数据D1已加共享锁，则T2可以对数据D1加共享锁，但不能加排它锁。事务T2对数据D2已加排他锁，则T1不能对D2加任何类型锁。</p>","multi":0,"questionType":1,"answer":"B","chooseItem":["794931255354347521"],"itemList":[{"id":"794931255337570305","questionId":"794931253466910721","content":"事务T1对数据D2加共享锁成功，加排它锁失败；事务T2对数据D1加共享锁成功、加排它锁失败","answer":0,"chooseValue":"A"},{"id":"794931255354347521","questionId":"794931253466910721","content":"事务T1对数据D2加排它锁和共享锁都失败；事务T2对数据D1加共享锁成功、加排它锁失败","answer":1,"chooseValue":"B"},{"id":"794931255383707649","questionId":"794931253466910721","content":"事务T1对数据D2加共享锁失败，加排它锁成功；事务T2对数据D1加共享锁成功、加排它锁失败","answer":0,"chooseValue":"C"},{"id":"794931255404679169","questionId":"794931253466910721","content":"事务T1对数据D2加共享锁成功，加排它锁失败；事务T2对数据D1加共享锁和排它锁都失败","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931236303818753","title":"<p>给定关系模式 R<U,F>;其中 U 为属性集，F 是 U 上的一组函数依赖，那么 Armstroog 公理系统的增广律是指（ ）。 </p>","analyze":"<p>试题分析：</p><p>Armstrong 公理函数依赖的推理规则有以下三条：</p><p>自反律：若属性集Y 包含于属性集X，属性集X 包含于U，则X→Y 在R 上成立。(此处X→Y是平凡函数依赖)</p><p>增广律：若X→Y 在R 上成立，且属性集Z 包含于属性集U，则XZ→YZ 在R 上成立。</p><p>传递律：若X→Y 和 Y→Z在R 上成立，则X →Z 在R 上成立。</p><p>其他的所有函数依赖的推理规则可以使用这三条规则推导出。</p>","multi":0,"questionType":1,"answer":"D","chooseItem":["794931238208032769"],"itemList":[{"id":"794931238153506817","questionId":"794931236303818753","content":"若 X→Y，X→Z，则 X→YZ 为 F 所蕴涵","answer":0,"chooseValue":"A"},{"id":"794931238174478337","questionId":"794931236303818753","content":"若 X→Y，WY→Z，则 XW→Z 为 F 所蕴涵","answer":0,"chooseValue":"B"},{"id":"794931238191255553","questionId":"794931236303818753","content":"若 X→Y，Y→Z 为 F 所蕴涵，则 X→Z 为 F 所蕴涵","answer":0,"chooseValue":"C"},{"id":"794931238208032769","questionId":"794931236303818753","content":"若 X→Y，为 F 所蕴涵，且 Z⊆U,则入 XZ→YZ 为 F 所蕴涵","answer":1,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931017327595521","title":"<p><br/></p><p class=\"MsoNormal\"><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">给定关系模式</span>R(A1，A2，A3，A4)，R上的函数依赖集F={A1A3→A2，A2→A3}，则R</span><span style=\"text-decoration:underline;\"><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">（</span>42）</span></span><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">。</span></span></p>","analyze":"<p><br/></p><p class=\"MsoNormal\" style=\"text-indent: 21pt; line-height: 150%;\"><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\">A1A3→A2，A2→A3，没有出现A4，所以候选关键字中肯定包A4，属性A1A3A4决定全属性，故为候选关键字。同理A1A2A4也为候选关键字。</span><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"></span></p><p class=\"MsoNormal\" style=\"text-indent: 21pt; line-height: 150%;\"><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"><span style=\"font-family:宋体\">设</span>U1={A1，A2}，U2={A1，A3}，那么可得出：U1∩U2→(U1-U2)=A1→A2，U1∩U2→(U2-U1)=A1→A3，而A1-A2，A1-A3∉F+，所以分解ρ是有损连接的。</span><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"></span></p><p class=\"MsoNormal\" style=\"line-height: 150%;\"><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"><span style=\"font-family:宋体\">又因为</span>F1=F2=∅， F+≠(F1∪F2)+，所以分解不保持函数依赖。</span><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"></span></p><p class=\"MsoNormal\"><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">参考答案：</span></span><span style=\"font-family: 宋体; font-size: 10.5pt;\">(42)</span><span style=\"font-family: 宋体; font-size: 10.5pt;\">C</span><span style=\"font-family: 宋体; font-size: 10.5pt;\"> </span></p>","multi":0,"questionType":1,"answer":"C","chooseItem":["794931019252781057"],"itemList":[{"id":"794931019215032321","questionId":"794931017327595521","content":"有一个候选关键字A1A3","answer":0,"chooseValue":"A"},{"id":"794931019236003841","questionId":"794931017327595521","content":"有一个候选关键字A1A2A3","answer":0,"chooseValue":"B"},{"id":"794931019252781057","questionId":"794931017327595521","content":"有两个候选关键字A1A3A4和A1A2A4","answer":1,"chooseValue":"C"},{"id":"794931019269558273","questionId":"794931017327595521","content":"有三个候选关键字A1A2、A1A3和A1A4","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931094754447361","title":"<p>给定关系R（A,B,C,D,E）与S（A,B,C,F,G），那么与表达式<img style=\"max-width:100%;height:auto\" src=\"https://image.chaiding.com/ruankao/876640779e8b17edb1c378c57b36b94b.png?x-oss-process=style/ruankaodaren\" title=\"876640779e8b17edb1c378c57b36b94b.png\" alt=\"blob.png\"/>等价的SQL语句如下：select （作答此空） from R, S where （）。</p>","analyze":"<p>本题考查关系代数运算与SQL语言的对应关系，注意本题中R与S是做自然连接操作，操作时会将R与S中相同字段名做等值连接，并将结果集去重复。所以R与S自然连接后的结果包括以下属性：</p><p>R.A，R.B，R.C，D，E，F，G。</p><p>关系代数选择条件为“1<6”，即R.A<F。</p><p>关系代数投影操作条件为“1,2,4,6,7”，对应的属性为R.A，R.B，D，F，G。</p><p><br/></p>","multi":0,"questionType":1,"answer":"B","chooseItem":["794931096633495553"],"itemList":[{"id":"794931096608329729","questionId":"794931094754447361","content":"R.A，R.B，R.E，S.C，G","answer":0,"chooseValue":"A"},{"id":"794931096633495553","questionId":"794931094754447361","content":"R.A，R.B，D，F，G","answer":1,"chooseValue":"B"},{"id":"794931096654467073","questionId":"794931094754447361","content":"R.A，R.B，R.D，S.C，F","answer":0,"chooseValue":"C"},{"id":"794931096679632897","questionId":"794931094754447361","content":"R.A，R.B，R.D，S.C，G","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931073598377985","title":"<p><br/></p><p class=\"MsoNormal\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:Calibri;mso-hansi-font-family:Calibri;mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">在分布式数据库中有分片透明、复制透明、位置透明和逻辑透明等基本概念，其中：</span></span><span style=\"text-decoration:underline;\"><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">（ </span><span style=\"font-family:宋体\">）</span></span></span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:Calibri;mso-hansi-font-family:Calibri;mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">是指局部数据模型透明，即用户或应用程序无须知道局部使用的是哪种数据模型</span></span></p>","analyze":"<p><span style=\"font-family: 宋体; font-size: 10.5pt; text-indent: 20.7pt;\">本题考查分布式数据库基本概念。分片透明是指用户或应用程序不需要知道逻辑上访问的表具体是怎么分块存储的。复制透明是指采用复制技术的分布方法，用户不需要知道数据是复制到哪些节点，如何复制的。位置透明是指用户无须知道数据存放的物理位置，逻辑透明，即局部数据模型透明，是指用户或应用程序无须知道局部场地使用的是哪种数据模型。</span><br/></p><p class=\"MsoNormal\" style=\"text-indent:20.7000pt;\"><span style=\"mso-spacerun:'yes';font-family:Calibri;mso-fareast-font-family:宋体;mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p>","multi":0,"questionType":1,"answer":"D","chooseItem":["794931075557117953"],"itemList":[{"id":"794931075502592001","questionId":"794931073598377985","content":"分片透明","answer":0,"chooseValue":"A"},{"id":"794931075523563521","questionId":"794931073598377985","content":"复制透明","answer":0,"chooseValue":"B"},{"id":"794931075540340737","questionId":"794931073598377985","content":"位置透明","answer":0,"chooseValue":"C"},{"id":"794931075557117953","questionId":"794931073598377985","content":"逻辑透明","answer":1,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931014341251073","title":"<p><br/></p><p class=\"MsoNormal\"><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">数据挖掘的分析方法可以划分为关联分析、序列模式分析、分类分析和聚类分析四种。如果某方法需要一个示例库（该库中的每个元组都有一个给定的类标识）做训练集时，这种分析方法属于</span></span><span style=\"text-decoration:underline;\"><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">（</span>41）</span></span><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">。</span></span></p>","analyze":"<p><span style=\"font-family:宋体\">从功能上可以将数据挖掘的分析方法划分为四种，即关联</span><span style=\"font-family: 宋体; font-size: 10.5pt; text-indent: 20.7pt;\">(Associations)分析、序列模式(Sequential Patterns)分析、分类(Classifiers)分析和聚类(Clustering)分析。</span><br/></p><p class=\"MsoNormal\" style=\"text-indent: 20.7pt; line-height: 150%;\"><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"> <span style=\"font-family:宋体\">关联分析、序列分析、分类分析、聚类分析的基本思想为：。</span> </span><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"></span></p><p class=\"MsoNormal\" style=\"text-indent: 20.7pt; line-height: 150%;\"><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"><span style=\"font-family:宋体\">（</span>1）关联分析。关联分析主要用于发现不同事件之间的关联性，即一个事件发生的同时，另一个事件也经常发生。关联分析的重点在于快速发现那些有实用价值的关联发生的事件。其主要依据是事件发生的概率和条件概率应该符合一定的统计意义。在进行关联分析的同时，还需要计算两个参数，分别是最小置信度（可信度）和最小支持度，前者表示规则需满足的最低可靠度，用以过滤掉可能性过小的规则；后者则用来表示规则在统计意义上需满足的最小程度。</span><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"></span></p><p class=\"MsoNormal\" style=\"text-indent: 20.7pt; line-height: 150%;\"><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"><span style=\"font-family:宋体\">（</span>2）序列分析。序列分析主要用于发现一定时间间隔内接连发生的事件，这些事件构成一个序列，发现的序列应该具有普遍意义，其依据除了统计上的概率之外，还要加上时间的约束。在进行序列分析时，也应计算置信度和支持度。</span><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"></span></p><p class=\"MsoNormal\" style=\"text-indent: 20.7pt; line-height: 150%;\"><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"><span style=\"font-family:宋体\">（</span>3）分类分析。分类分析通过分析具有类别的样本特点，得到决定样本属于各种类别的规则或方法。利用这些规则和方法对未知类别的样本分类时应该具有一定的准确度。其主要方法有基于统计学的贝叶斯方法、神经网络方法、决策树方法等。分类分析时首先为每个记录赋予一个标记（一组具有不同特征的类别），即按标记分类记录，然后检查这些标定的记录，描述出这些记录的特征。这些描述可能是显式的，例如，一组规则定义；也可能是隐式的，例如，一个数学模型或公式。</span><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"></span></p><p class=\"MsoNormal\" style=\"text-indent: 20.7pt; line-height: 150%;\"><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"><span style=\"font-family:宋体\">（</span>4）聚类分析。聚类分析是根据“物以类聚”的原理，将本身没有类别的样本聚集成不同的组，并且对每个这样的组进行描述的过程。其主要依据是聚集到同一个组中的样本应该彼此相似，而属于不同组的样本应该足够不相似。聚类分析法是分类分析法的逆过程，它的输入集是一组未标定的记录，即输入的记录没有作任何处理，目的是根据一定的规则，合理地划分记录集合，并用显式或隐式的方法描述不同的类别。</span><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"></span></p><p class=\"MsoNormal\" style=\"line-height: 150%;\"><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"><span style=\"font-family:宋体\">在实际应用的</span>DM系统中，上述四种分析方法有着不同的适用范围，因此经常被综合运用。</span><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"></span></p><p class=\"MsoNormal\" style=\"line-height: 150%;\"><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"><span style=\"font-family:宋体\">参考答案：</span></span><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\">(41)</span><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\">C</span><span style=\"font-family: 宋体; line-height: 150%; font-size: 10.5pt;\"></span></p>","multi":0,"questionType":1,"answer":"C","chooseItem":["794931016400654337"],"itemList":[{"id":"794931016358711297","questionId":"794931014341251073","content":"关联分析","answer":0,"chooseValue":"A"},{"id":"794931016383877121","questionId":"794931014341251073","content":"序列模式分析","answer":0,"chooseValue":"B"},{"id":"794931016400654337","questionId":"794931014341251073","content":"分类分析","answer":1,"chooseValue":"C"},{"id":"794931016417431553","questionId":"794931014341251073","content":"聚类分析","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931035849641985","title":"<p><br/></p><p class=\"MsoNormal\"><span style=\"mso-spacerun:'yes';font-family:宋体;font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">给定关系模式</span>R(U,F)，U={A,B,C,D}，F={AB→C,CD→B}。关系R</span><span style=\"text-decoration:underline;\"><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">（</span>42）。</span></span></p>","analyze":"<p><br/></p><p class=\"MsoNormal\" style=\"margin-left: 0pt; text-indent: 21pt; line-height: 150%;\"><span style=\"mso-spacerun:'yes';font-family:宋体;line-height:150%;font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">根据函数依赖定义，可知</span>ACD→U ,ABD→U,所以ACD和ABD均为候选关键字。</span><span style=\"mso-spacerun:'yes';font-family:宋体;line-height:150%;font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p><p class=\"MsoNormal\" style=\"margin-left: 0pt; text-indent: 0pt; line-height: 150%;\"><span style=\"mso-spacerun:'yes';font-family:宋体;line-height:150%;font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">根据主属性的定义</span>“包含在任何一个候选码中的属性叫做主属性(Prime attribute), 否则叫做非主属性（Nonprime attribute)”，所以，关系R中的4个属性都是主属性。</span><span style=\"mso-spacerun:'yes';font-family:宋体;line-height:150%;font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p><p class=\"MsoNormal\"><span style=\"font-family: 宋体; font-size: 10.5pt; background: #7F7F7F;\"><span style=\"font-family:宋体\">参考答案</span></span><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">：</span></span><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">（</span></span><span style=\"font-family: 宋体; font-size: 10.5pt;\">42）C </span></p>","multi":0,"questionType":1,"answer":"C","chooseItem":["794931037766438913"],"itemList":[{"id":"794931037728690177","questionId":"794931035849641985","content":"只有1个候选关键字ACB","answer":0,"chooseValue":"A"},{"id":"794931037745467393","questionId":"794931035849641985","content":"只有1个候选关键字BCD","answer":0,"chooseValue":"B"},{"id":"794931037766438913","questionId":"794931035849641985","content":"有2个候选关键字ACD和ABD","answer":1,"chooseValue":"C"},{"id":"794931037783216129","questionId":"794931035849641985","content":"有2个候选关键字ACB和BCD","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931147653009409","title":"若要使某用户只能查询表EMP中的部分记录，应采取的策略是（）。","analyze":"<p>选项A是错误的，因为具有DBA特权的用户可操作数据库的所有资源。</p><p>选项B是错误的，因为选项B是将表EMP的查询权限赋予该用户，即全部记录，而题目只允许某用户查询表EMP中的部分记录。</p><p>选项C是误的，因为编写查询表EMP的存储过程仍然是查询表EMP的所有记录。</p><p>选项D是正确的，因为是构建该部分记录的行级视图，并将该视图的查询权限赋予该用户。</p>","multi":0,"questionType":1,"answer":"D","chooseItem":["794931149561417729"],"itemList":[{"id":"794931149502697473","questionId":"794931147653009409","content":"将该用户级别设定为DBA","answer":0,"chooseValue":"A"},{"id":"794931149519474689","questionId":"794931147653009409","content":"将表EMP的查询权限赋予该用户","answer":0,"chooseValue":"B"},{"id":"794931149540446209","questionId":"794931147653009409","content":"编写查询表EMP的存储过程","answer":0,"chooseValue":"C"},{"id":"794931149561417729","questionId":"794931147653009409","content":"构建该部分记录的行级视图，并将该视图的查询权限赋予该用户","answer":1,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931070561701889","title":"<p><img style=\"max-width:100%;height:auto\" src=\"https://image.chaiding.com/ruankao/35ca41b5e672ecc8673107b0502d224d.png?x-oss-process=style/ruankaodaren\" title=\"35ca41b5e672ecc8673107b0502d224d.png\" alt=\"image.png\"/>运算<br/><img style=\"max-width:100%;height:auto\" src=\"https://image.chaiding.com/ruankao/0aa6f3704d94bf13a3451b0b2c8919c2.png?x-oss-process=style/ruankaodaren\" title=\"0aa6f3704d94bf13a3451b0b2c8919c2.png\" alt=\"image.png\"/></p>","analyze":"<p><span style=\"font-family: 宋体; font-size: 12pt;\">选项中几个条件都是正确的，需要选择的，其实只是使用AND还是OR来进行连接。由于进行自然连接以及相关条件判断都是同时要成立的，所以必须都要用AND进行连接。</span><br/></p><p class=\"MsoNormal\"><span style=\"mso-spacerun:'yes';font-family:Calibri;mso-fareast-font-family:宋体;mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p>","multi":0,"questionType":1,"answer":"C","chooseItem":["794931072491081729"],"itemList":[{"id":"794931072457527297","questionId":"794931070561701889","content":"A","answer":0,"chooseValue":"A"},{"id":"794931072474304513","questionId":"794931070561701889","content":"B","answer":0,"chooseValue":"B"},{"id":"794931072491081729","questionId":"794931070561701889","content":"C","answer":1,"chooseValue":"C"},{"id":"794931072512053249","questionId":"794931070561701889","content":"D","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931268163751937","title":"<p>在设计关系模式时，有时为了提高数据操作的性能，会故意增加冗余数据，使得关系模式不满足 3NF 或 BCNF，这种方法称之为反规范化，下列不属于反规范化手段的是（ ）。</p>","analyze":"<p>在设计关系模式时，有时为了提高数据操作的性能，会故意增加冗余数据，使得关系模式不满足 3NF或 BCNF，这种方法称之为反规范化。</p><p>常见的范规范化手段有增加冗余属性、增加派生属性、合并模式和分割模式等。<br/></p>","multi":0,"questionType":1,"answer":"C","chooseItem":["794931270516756481"],"itemList":[{"id":"794931270483202049","questionId":"794931268163751937","content":"合并模式","answer":0,"chooseValue":"A"},{"id":"794931270499979265","questionId":"794931268163751937","content":"增加冗余属性","answer":0,"chooseValue":"B"},{"id":"794931270516756481","questionId":"794931268163751937","content":"创建视图","answer":1,"chooseValue":"C"},{"id":"794931270546116609","questionId":"794931268163751937","content":"增加派生属性","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931173645111297","title":"<p><strong>请作答第<span style=\"color: red\">1</span>空。</strong></p><p>在数据库设计的需求分析阶段应当形成（41），这些文档可以作为（42）阶段的设计依据。</p>","analyze":"数据库设计主要分为用户需求分析、概念结构、逻辑结构和物理结构设计四个阶段。其中，在用户需求分析阶段中，数据库设计人员采用一定的辅助工具对应用对象的功能、性能、 限制等要求所进行的科学分析，并形成需求说明文档、数据字典和数据流程图。用户需求分析阶段形成的相关文档用以作为概念结构设计的设计依据。","multi":0,"questionType":1,"answer":"C","chooseItem":["794931175557713921"],"itemList":[{"id":"794931175507382273","questionId":"794931173645111297","content":"程序文档、数据字典和数据流图","answer":0,"chooseValue":"A"},{"id":"794931175532548097","questionId":"794931173645111297","content":"需求说明文档、程序文档和数据流图","answer":0,"chooseValue":"B"},{"id":"794931175557713921","questionId":"794931173645111297","content":"需求说明文档、数据字典和数据流图","answer":1,"chooseValue":"C"},{"id":"794931175578685441","questionId":"794931173645111297","content":"需求说明文档、数据字典和程序文档","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931153281765377","title":"<p><strong>请作答第<span style=\"color: red\">1</span>空。</strong></p><p>某公司的商品(商品号，商品名称，生产商，单价)和仓库(仓库号，地址，电话，商品号，库存量)两个实体之间的关系如表1和表2所示。</p><p><img style=\"max-width:100%;height:auto\" src=\"https://image.chaiding.com/ruankao/19112328b1daaebc7e98e51484404353.jpg?x-oss-process=style/ruankaodaren\" title=\"19112328b1daaebc7e98e51484404353.jpg\" alt=\"1.jpg\"/></p><p>商品关系的主键是 （34）；仓库关系的主键是（35）；仓库关系 （36） ，为了解决这一问题，需要将仓库关系分解为 （37） 。<br/></p>","analyze":"商品关系的主键是商品号，仓库关系的主键是(仓库号，商品号)。显然，仓库关系存在冗余、修改操作的不一致，以及插入异常和删除异常。例如，仓库号为“01”的商品有3种，其地址就要重复3次，故存在冗余。为了解决仓库关系模式存在的问题，就需要进行模式分解，其中（37）空选项A存在非主属性对主键的部分函数依赖，即“仓库号→电话”。选项B存在的问题是分解属于有损联接，即分解的新关系模式仓库1和仓库2无法恢复到原关系。选项C分解存在的问题与A类同。","multi":0,"questionType":1,"answer":"A","chooseItem":["794931155135647745"],"itemList":[{"id":"794931155135647745","questionId":"794931153281765377","content":"商品号","answer":1,"chooseValue":"A"},{"id":"794931155152424961","questionId":"794931153281765377","content":"商品名称","answer":0,"chooseValue":"B"},{"id":"794931155169202177","questionId":"794931153281765377","content":"生产商","answer":0,"chooseValue":"C"},{"id":"794931155185979393","questionId":"794931153281765377","content":"单价","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931256360980481","title":"<p><strong>请作答第<span style=\"color: red\">1</span>空。</strong></p><p>若要将部门表Demp中name列的查询权限赋予用户XiaoLi。并允许XiaoLi将该限授予他人。实现的SQL语句如下：</p><p>GRANT （18） ON TABLE Demp TO XiaoLi （19） 。</p>","analyze":"<p>授权语句GRANT的格式为：</p><p>GRANT <权限> [，<权限>]…</p><p>[ON <对象类型><对象名>]</p><p>TO <用户>[，<用户>]…</p><p>[WITH GRANT OPTION]；</p><p>WITH GRANT OPTION的作用是权限传递，既允许用户将其权限分配给其他用户。所以（45）空为WITH GRANT OPTION。</p><p>由于题目要求传递的权限是name列的查询权限，所以空（18）为SELECT （name）。</p>","multi":0,"questionType":1,"answer":"C","chooseItem":["794931258361663489"],"itemList":[{"id":"794931258328109057","questionId":"794931256360980481","content":"QUERY（name）","answer":0,"chooseValue":"A"},{"id":"794931258344886273","questionId":"794931256360980481","content":"SEARCH （name）","answer":0,"chooseValue":"B"},{"id":"794931258361663489","questionId":"794931256360980481","content":"SELECT（name）","answer":1,"chooseValue":"C"},{"id":"794931258374246401","questionId":"794931256360980481","content":"ALL PRIVILEGES（name）","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931213780406273","title":"<p><strong>请作答第<span style=\"color: red\">1</span>空。</strong></p><p>设ρ={（A1，A2），（A1，A3）}是关系R（A1,A2,A3）上的一个分解，下表是R上的一个关系实例r，R的函数依赖集为（ ），分解ρ（ ）。</p><img style=\"max-width:100%;height:auto\" src=\"https://image.chaiding.com/ruankao/e1f95518f8403d31d65fdc376ce621db.jpg?x-oss-process=style/ruankaodaren\" title=\"e1f95518f8403d31d65fdc376ce621db.jpg\" alt=\"1.jpg\"/>","analyze":"A1A3可以唯一确定一个A2，例如，A1=a，A3=d，可以确定A2=a。同理A1A2也能唯一确定一个A3。U1∩U2=A1，A1无法推出A2、A3，所以属于有损连接。该分解也不保持函数依赖具体可参考51CTO相关视频课程。","multi":0,"questionType":1,"answer":"D","chooseItem":["794931215672037377"],"itemList":[{"id":"794931215630094337","questionId":"794931213780406273","content":"F={A1→A2,A1→A3}","answer":0,"chooseValue":"A"},{"id":"794931215642677249","questionId":"794931213780406273","content":"F={A1→A2}","answer":0,"chooseValue":"B"},{"id":"794931215655260161","questionId":"794931213780406273","content":"F={A1→A3}","answer":0,"chooseValue":"C"},{"id":"794931215672037377","questionId":"794931213780406273","content":"F={A1A3→A2,A1A2→A3}","answer":1,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931191147941889","title":"<p><strong>请作答第<span style=\"color: red\">1</span>空。</strong></p>设有职工实体 Employee （职工号，姓名，性别，年龄，通信地址，家庭成员），其中通信地址记录了邮编、省、市、街道信息;家庭成员记录了职工的亲属的姓名。职工实体中的通信地址是一个（23）属性;为了将数据库模式设计的更合理，对于家庭成员属性（24）。","analyze":"本题职工实体集Employee的通信地址可以进一步分为邮编、省、市、街道。属于符合属性。为了将数据库模式设计的更合理，对于家庭成员属性应该将职工亲属的姓名加上职工号设计成为一个独立的实体。否则会职工实体有数据冗余等问题的产生。","multi":0,"questionType":1,"answer":"B","chooseItem":["794931193026990081"],"itemList":[{"id":"794931193010212865","questionId":"794931191147941889","content":"简单","answer":0,"chooseValue":"A"},{"id":"794931193026990081","questionId":"794931191147941889","content":"复合","answer":1,"chooseValue":"B"},{"id":"794931193043767297","questionId":"794931191147941889","content":"多值","answer":0,"chooseValue":"C"},{"id":"794931193060544513","questionId":"794931191147941889","content":"派生","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931164979679233","title":"<p><strong>请作答第<span style=\"color: red\">1</span>空。</strong></p><p>建立一个供应商、零件数据库。其中“供应商”表S(Sno，Sname，Zip，City)中的元素分别表示供应商代码、供应商名、供应商邮编、供应商所在城市，其函数依赖为：Sno→(Sname，Zip，City)，Zip→City。</p><p>a. “供应商”表S属于（38）。</p><p>b.若要求：供应商代码不能为空，且值是唯一的，供应商的名也是唯一的：零件号不能为空，且值是唯—的；一个供应商可以供应多种零件，而一种零件可以由多个供应商供应。请将下面的SQL语句空缺部分补充完整。</p><p>CREATE TABLE S(Sno CHAR(5) (39),</p><p>Sname CHAR(30) UNIQUE,</p><p>Zip CHAR(8),</p><p>City CHAR(20),</p><p>（40）;</p>","analyze":"<p>"供应商"表S属于2NF，因为表S的主键是Sno，非主属性Sname，Zip，City不存在对主键的部分函数依赖。但是，当2NF消除了非主属性对主键的传递函数依赖，则称为3NF。"供应商"表S不属于 3NF，因为存在传递依赖，即Sno→ Zip，Zip →City。所以正确的答案是B。</p><p>要求供应商代码不能为空，且值是唯一的，供应商的名也是唯一的，所以需要用NOT NULL UNIQUE。试题（44）正确的答案是C，因为表S的主键是Sno，所以需要用PRIMARY KEY（Sno）来约束。补充完整的SQL语句如下∶</p><p>CREATE TABLE S (Sno CHAR (5)NOT NULL UNIQUE,</p><p>Sname CHAR (30) UNIQUE,</p><p>ZIP CHAR(8),</p><p>City CHAR(20)</p><p>PRIMARY KEY(Sno));</p>","multi":0,"questionType":1,"answer":"B","chooseItem":["794931166888087553"],"itemList":[{"id":"794931166858727425","questionId":"794931164979679233","content":"1NF","answer":0,"chooseValue":"A"},{"id":"794931166888087553","questionId":"794931164979679233","content":"2NF","answer":1,"chooseValue":"B"},{"id":"794931166913253377","questionId":"794931164979679233","content":"3NF","answer":0,"chooseValue":"C"},{"id":"794931166938419201","questionId":"794931164979679233","content":"BCNF","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931208080347137","title":"<p><strong>请作答第<span style=\"color: red\">1</span>空。</strong></p><p>某商场商品数据库的商品关系模式P(商品代码，商品名称，供应商，联系方式，库存量)，函数依赖集F={商品代码→商品名称，(商品代码，供应商)→库存量，供应商→联系方式}。商品关系模式P达到（）；该关系模式分解成（）后，具有无损连接的特性，并能够保持函数依赖。</p>","analyze":"<p>根据题意，零件P关系中的(商品代码，供应商)可决定的零件P关系的所有属性，所以零件P关系的主键为(商品代码，供应商)；又因为，根据题意(商品代码，供应商)→商品名称，而商品代码→商品名称，存在部分依赖关系不满足2NF，因此该关系模式属于1NF。</p><p>由于关系模式P属于1NF，1NF存在冗余度大、修改操作的不一致性、插入异常和删除异常四个问题。所以需要对模式分解，其中选项A、选项B和选项C分解后的P1∩P2=∅，是有损连接，并且分解后的关系式丢失了函数依赖，如选项A中的P1(商品代码，联系方式)与原F关系式中的“商品代码→商品”不相符，即不保持函数依赖。</p>","multi":0,"questionType":1,"answer":"A","chooseItem":["794931209930035201"],"itemList":[{"id":"794931209930035201","questionId":"794931208080347137","content":"1NF","answer":1,"chooseValue":"A"},{"id":"794931209959395329","questionId":"794931208080347137","content":"2NF","answer":0,"chooseValue":"B"},{"id":"794931209984561153","questionId":"794931208080347137","content":"3NF","answer":0,"chooseValue":"C"},{"id":"794931210005532673","questionId":"794931208080347137","content":"BCNF","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931199624630273","title":"<p><strong>请作答第<span style=\"color: red\">1</span>空。</strong></p><p>分布式数据库系统除了包含集中式数据库系统的模式结构之外，还增加了几个模式级别，其中 (41) 定义分布式数据库中数据的整体逻辑结构，使得数据使用方便，如同没有分布一样。（42）是指用户或应用程序无需知道局部使用的是哪种数据模型。</p>","analyze":"<p>本题考查分布式数据库的基本概念。</p><p>分布式数据库在各结点上独立，在全局上统一。因此需要定义全局的逻辑结构，称之为全局概念模式，全局外模式是全局概念模式的子集，分片模式和分布模式分别描述数据在逻辑上的分片方式和在物理上各结点的分布形式。</p><p>物理位置，即位置透明性，要会联想记忆。</p><p>分片透明性：用户或应用程序不需要知道逻辑上访问的表具体是如何分块存储的。</p><p>位置透明性：应用程序不关心数据存储物理位置的改变。</p><p>逻辑透明性：用户或应用程序无需知道局部使用的是哪种数据模型。</p><p>复制透明性：用户或应用程序不关心复制的数据从何而来。</p>","multi":0,"questionType":1,"answer":"D","chooseItem":["794931201520455681"],"itemList":[{"id":"794931201474318337","questionId":"794931199624630273","content":"分片模式","answer":0,"chooseValue":"A"},{"id":"794931201491095553","questionId":"794931199624630273","content":"全局外模式","answer":0,"chooseValue":"B"},{"id":"794931201507872769","questionId":"794931199624630273","content":"分布模式","answer":0,"chooseValue":"C"},{"id":"794931201520455681","questionId":"794931199624630273","content":"全局概念模式","answer":1,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931136378720257","title":"<p><strong>请作答第<span style=\"color: red\">1</span>空。</strong></p><p>假设员工关系EMP(员工号，姓名，性别，部门，部门电话，部门负责人，家庭住址，家庭成员，成员关系)如下表所示。如果一个部门只能有一部电话和一位负责人，一个员工可以有多个家庭成员，那么关系EMP属于（1），且（2）问题；为了解决这一问题，应该将员工关系EMP分解为 （3）。</p><p><img style=\"max-width:100%;height:auto\" src=\"https://image.chaiding.com/ruankao/5683ec8aab542cfd66536e2454e3583e.jpg?x-oss-process=style/ruankaodaren\" title=\"5683ec8aab542cfd66536e2454e3583e.jpg\" alt=\"1.jpg\"/></p><br/>","analyze":"本题主键是（员工号、家庭成员）部门名等非主属性对其存在部分依赖，不符合2NF。","multi":0,"questionType":1,"answer":"A","chooseItem":["794931138240991233"],"itemList":[{"id":"794931138240991233","questionId":"794931136378720257","content":"1NF","answer":1,"chooseValue":"A"},{"id":"794931138266157057","questionId":"794931136378720257","content":"2NF","answer":0,"chooseValue":"B"},{"id":"794931138291322881","questionId":"794931136378720257","content":"3NF","answer":0,"chooseValue":"C"},{"id":"794931138316488705","questionId":"794931136378720257","content":"BCNF","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931179445833729","title":"<p><strong>请作答第<span style=\"color: red\">1</span>空。</strong></p><p>设有员工实体Employee （employeelD，name，sex，birth，age，tel，departID），其中employeelD为员工号，name为员工姓名，sex为员工性别，age为员工年龄，birth为员工出生日期，tel为员工电话，记录该员的手机号码、办公室电话等，deparlD为员工所在部门号，参照另一部门实体Department的主键departID。Employee实体中存在派生属性（19）。Employee实体中还存在多值属性（20）。对属性 departID的约束是（21）。</p>","analyze":"派生属性是指可以由其他属性经过运算得到的属性，因而派生属性产生冗余，通常不存储，如本题的age;多值属性是指一个实体在该属性上会同时取多个属性，这些值也都必须存储，如本题的tel。数据约束也是描述用户信息的，根据参照完整性约束的定义，Employee实体中的departID属性应为外键。","multi":0,"questionType":1,"answer":"B","chooseItem":["794931181350047745"],"itemList":[{"id":"794931181316493313","questionId":"794931179445833729","content":"name，原因是会存在同名员工","answer":0,"chooseValue":"A"},{"id":"794931181350047745","questionId":"794931179445833729","content":"age，原因是用属性birth替换age并可计算age","answer":1,"chooseValue":"B"},{"id":"794931181379407873","questionId":"794931179445833729","content":"tel，原因是员工有多个电话","answer":0,"chooseValue":"C"},{"id":"794931181412962305","questionId":"794931179445833729","content":"departID，原因是实体Department已有departID","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931244960862209","title":"<p><strong>请作答第<span style=\"color: red\">1</span>空。</strong></p><p>给定关系模式R(U,F)，U={A1,A2,A3,A4}，F={A1A2→A3，A3→A4}，那么在关系R中 （15 ） 。以下说法错误的是 （16） 。</p>","analyze":"<p>由于A1A2→A3，A3→A4，根据传递性，A1A2→A4。而A1或者A2都不能推出A3或者A4。所以关系R有1个候选关键字A1A2。</p><p>\t由“A1A2→A3”，得不到“A1→A2A3”</p>","multi":0,"questionType":1,"answer":"A","chooseItem":["794931246844104705"],"itemList":[{"id":"794931246844104705","questionId":"794931244960862209","content":"有1个候选关键字A1A2","answer":1,"chooseValue":"A"},{"id":"794931246865076225","questionId":"794931244960862209","content":"有1个候选关键字A2A3","answer":0,"chooseValue":"B"},{"id":"794931246881853441","questionId":"794931244960862209","content":"有2个候选关键字A1和A2","answer":0,"chooseValue":"C"},{"id":"794931246898630657","questionId":"794931244960862209","content":"有2个候选关键字A1和A2A3","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931142032642049","title":"<p><strong>请作答第<span style=\"color: red\">1</span>空。</strong></p><p><br/></p><p> </p><p><br/></p><p><br/></p><p>关系R、S如下图所示，关系代数表达式π3,4,5(σ1＜6(R×S)= （1） ，对关系R、S进行自然连接后的属性列数和元组个数分别为（2）。</p><p><img style=\"max-width:100%;height:auto\" title=\"079474f420e87cca38cee47ba4ac5a2f.png\" alt=\"image.png\" src=\"https://image.chaiding.com/ruankao/079474f420e87cca38cee47ba4ac5a2f.png?x-oss-process=style/ruankaodaren\"/></p><br/>","analyze":"<p>R×S后的结果如表7.6所示。<br/></p><p><img style=\"max-width:100%;height:auto\" title=\"551abc158791ac6651a88311f6441edc.png\" alt=\"image.png\" src=\"https://image.chaiding.com/ruankao/551abc158791ac6651a88311f6441edc.png?x-oss-process=style/ruankaodaren\"/><br/></p><p>其中σ1＜6(R×S)表示选择R.A小于S.C的元组，结果如下表所示。</p><p><br/></p><p><img style=\"max-width:100%;height:auto\" title=\"3509550525ec560854999015ffd7b3e3.png\" alt=\"image.png\" src=\"https://image.chaiding.com/ruankao/3509550525ec560854999015ffd7b3e3.png?x-oss-process=style/ruankaodaren\"/><br/></p><p>将上述结果的3、4、5列进行投影</p><p><img style=\"max-width:100%;height:auto\" title=\"4d28e9a4d342483a74e54141b1e22907.png\" alt=\"image.png\" src=\"https://image.chaiding.com/ruankao/4d28e9a4d342483a74e54141b1e22907.png?x-oss-process=style/ruankaodaren\"/><br/></p><p>按选项要求整理后结果：</p><p><img style=\"max-width:100%;height:auto\" title=\"7f014c6005e3db466d4f35e0cd329970.png\" alt=\"image.png\" src=\"https://image.chaiding.com/ruankao/7f014c6005e3db466d4f35e0cd329970.png?x-oss-process=style/ruankaodaren\"/> <br/></p><p><br/></p><p><br/></p>","multi":0,"questionType":1,"answer":"B","chooseItem":["794931143899107329"],"itemList":[{"id":"794931143882330113","questionId":"794931142032642049","content":"<img style=\"max-width:100%;height:auto\" title=\"f520ab693cd4f94ad18f7556266ffaf2.jpg\" alt=\"1.jpg\" src=\"https://image.chaiding.com/ruankao/f520ab693cd4f94ad18f7556266ffaf2.jpg?x-oss-process=style/ruankaodaren\"/>","answer":0,"chooseValue":"A"},{"id":"794931143899107329","questionId":"794931142032642049","content":"<img style=\"max-width:100%;height:auto\" title=\"24815d611f765199dd12d41a2629da60.jpg\" alt=\"2.jpg\" src=\"https://image.chaiding.com/ruankao/24815d611f765199dd12d41a2629da60.jpg?x-oss-process=style/ruankaodaren\"/>","answer":1,"chooseValue":"B"},{"id":"794931143911690241","questionId":"794931142032642049","content":"<img style=\"max-width:100%;height:auto\" title=\"aed04538fe792e2664ae13c739e210f9.jpg\" alt=\"3.jpg\" src=\"https://image.chaiding.com/ruankao/aed04538fe792e2664ae13c739e210f9.jpg?x-oss-process=style/ruankaodaren\"/>","answer":0,"chooseValue":"C"},{"id":"794931143924273153","questionId":"794931142032642049","content":"<img style=\"max-width:100%;height:auto\" title=\"8725b1c7956c06d89b08f71e91e26db3.jpg\" alt=\"4.jpg\" src=\"https://image.chaiding.com/ruankao/8725b1c7956c06d89b08f71e91e26db3.jpg?x-oss-process=style/ruankaodaren\"/>","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931271485640705","title":"<p><strong>请作答第<span style=\"color: red\">1</span>空。</strong></p><p>分布式数据库系统除了包含集中式数据库系统的模式结构之外，还增加了几个模式级别，其中 () 定义分布式数据库中数据的整体逻辑结构，使得数据使用方便，如同没有分布一样。（）是指用户或应用程序无需知道局部使用的是哪种数据模型。</p>","analyze":"<p>本题考查分布式数据库的基本概念。</p><p>分布式数据库在各结点上独立，在全局上统一。因此需要定义全局的逻辑结构，称之为全局概念模式，全局外模式是全局概念模式的子集，分片模式和分布模式分别描述数据在逻辑上的分片方式和在物理上各结点的分布形式。</p><p>物理位置，即位置透明性，要会联想记忆。</p><p>分片透明性：用户或应用程序不需要知道逻辑上访问的表具体是如何分块存储的。</p><p>位置透明性：应用程序不关心数据存储物理位置的改变。</p><p>逻辑透明性：用户或应用程序无需知道局部使用的是哪种数据模型</p>","multi":0,"questionType":1,"answer":"D","chooseItem":["794931273482129409"],"itemList":[{"id":"794931273415020545","questionId":"794931271485640705","content":"分片模式","answer":0,"chooseValue":"A"},{"id":"794931273435992065","questionId":"794931271485640705","content":"全局外模式","answer":0,"chooseValue":"B"},{"id":"794931273456963585","questionId":"794931271485640705","content":"分布模式","answer":0,"chooseValue":"C"},{"id":"794931273482129409","questionId":"794931271485640705","content":"全局概念模式","answer":1,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931280444674049","title":"<p><strong>请作答第<span style=\"color: red\">1</span>空。</strong></p><p>某商场商品数据库的商品关系模式P(商品代码，商品名称，供应商，联系方式，库存量)，函数依赖集F={商品代码→商品名称，(商品代码，供应商)→库存量，供应商→联系方式}。商品关系模式P达到（ ）；该关系模式分解成（ ）后，具有无损连接的特性，并能够保持函数依赖。</p>","analyze":"<p>根据题意，零件P关系中的(商品代码，供应商)可决定的零件P关系的所有属性，所以零件P关系的主键为(商品代码，供应商)；又因为，根据题意(商品代码，供应商)→商品名称，而商品代码→商品名称，存在部分依赖关系不满足2NF，因此该关系模式属于1NF。</p><p>由于关系模式P属于1NF，1NF存在冗余度大、修改操作的不一致性、插入异常和删除异常四个问题。所以需要对模式分解，其中选项A、选项B和选项C分解后的P1∩P2=?，是有损连接，并且分解后的关系式丢失了函数依赖，如选项A中的P1(商品代码，联系方式)与原F关系式中的“商品代码→商品”不相符，即不保持函数依赖。</p>","multi":0,"questionType":1,"answer":"A","chooseItem":["794931282323722241"],"itemList":[{"id":"794931282323722241","questionId":"794931280444674049","content":"1NF","answer":1,"chooseValue":"A"},{"id":"794931282340499457","questionId":"794931280444674049","content":"2NF","answer":0,"chooseValue":"B"},{"id":"794931282361470977","questionId":"794931280444674049","content":"3NF","answer":0,"chooseValue":"C"},{"id":"794931282378248193","questionId":"794931280444674049","content":"BCNF","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931283334549505","title":"<p><strong>请作答第<span style=\"color: red\">2</span>空。</strong></p><p>某商场商品数据库的商品关系模式P(商品代码，商品名称，供应商，联系方式，库存量)，函数依赖集F={商品代码→商品名称，(商品代码，供应商)→库存量，供应商→联系方式}。商品关系模式P达到（ ）；该关系模式分解成（ ）后，具有无损连接的特性，并能够保持函数依赖。</p>","analyze":"<p>根据题意，零件P关系中的(商品代码，供应商)可决定的零件P关系的所有属性，所以零件P关系的主键为(商品代码，供应商)；又因为，根据题意(商品代码，供应商)→商品名称，而商品代码→商品名称，存在部分依赖关系不满足2NF，因此该关系模式属于1NF。</p><p>由于关系模式P属于1NF，1NF存在冗余度大、修改操作的不一致性、插入异常和删除异常四个问题。所以需要对模式分解，其中选项A、选项B和选项C分解后的P1∩P2=?，是有损连接，并且分解后的关系式丢失了函数依赖，如选项A中的P1(商品代码，联系方式)与原F关系式中的“商品代码→商品”不相符，即不保持函数依赖。</p>","multi":0,"questionType":1,"answer":"D","chooseItem":["794931285293289473"],"itemList":[{"id":"794931285209403393","questionId":"794931283334549505","content":"P1(商品代码，联系方式)，P2(商品名称，供应商，库存量)","answer":0,"chooseValue":"A"},{"id":"794931285238763521","questionId":"794931283334549505","content":"P1(商品名称，联系方式)，P2(商品代码，供应商，库存量)","answer":0,"chooseValue":"B"},{"id":"794931285263929345","questionId":"794931283334549505","content":"P1(商品代码，商品名称，联系方式)，P2(供应商，库存量)","answer":0,"chooseValue":"C"},{"id":"794931285293289473","questionId":"794931283334549505","content":"P1(商品代码，商品名称)，P2(商品代码，供应商，库存量)，P3(供应商，联系方式)","answer":1,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931176497238017","title":"<p><strong>请作答第<span style=\"color: red\">2</span>空。</strong></p><p>在数据库设计的需求分析阶段应当形成（41），这些文档可以作为（42）阶段的设计依据。</p>","analyze":"数据库设计主要分为用户需求分析、概念结构、逻辑结构和物理结构设计四个阶段。其中，在用户需求分析阶段中，数据库设计人员采用一定的辅助工具对应用对象的功能、性能、 限制等要求所进行的科学分析，并形成需求说明文档、数据字典和数据流程图。用户需求分析阶段形成的相关文档用以作为概念结构设计的设计依据。","multi":0,"questionType":1,"answer":"B","chooseItem":["794931178397257729"],"itemList":[{"id":"794931178380480513","questionId":"794931176497238017","content":"逻辑结构设计","answer":0,"chooseValue":"A"},{"id":"794931178397257729","questionId":"794931176497238017","content":"概念结构设计","answer":1,"chooseValue":"B"},{"id":"794931178418229249","questionId":"794931176497238017","content":"物理结构设计","answer":0,"chooseValue":"C"},{"id":"794931178439200769","questionId":"794931176497238017","content":"数据库运行和维护","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931210924085249","title":"<p><strong>请作答第<span style=\"color: red\">2</span>空。</strong></p><p>某商场商品数据库的商品关系模式P(商品代码，商品名称，供应商，联系方式，库存量)，函数依赖集F={商品代码→商品名称，(商品代码，供应商)→库存量，供应商→联系方式}。商品关系模式P达到（）；该关系模式分解成（）后，具有无损连接的特性，并能够保持函数依赖。</p>","analyze":"<p>根据题意，零件P关系中的(商品代码，供应商)可决定的零件P关系的所有属性，所以零件P关系的主键为(商品代码，供应商)；又因为，根据题意(商品代码，供应商)→商品名称，而商品代码→商品名称，存在部分依赖关系不满足2NF，因此该关系模式属于1NF。</p><p>由于关系模式P属于1NF，1NF存在冗余度大、修改操作的不一致性、插入异常和删除异常四个问题。所以需要对模式分解，其中选项A、选项B和选项C分解后的P1∩P2=∅，是有损连接，并且分解后的关系式丢失了函数依赖，如选项A中的P1(商品代码，联系方式)与原F关系式中的“商品代码→商品”不相符，即不保持函数依赖。</p>","multi":0,"questionType":1,"answer":"D","chooseItem":["794931212861853697"],"itemList":[{"id":"794931212794744833","questionId":"794931210924085249","content":"P1(商品代码，联系方式)，P2(商品名称，供应商，库存量)","answer":0,"chooseValue":"A"},{"id":"794931212819910657","questionId":"794931210924085249","content":"P1(商品名称，联系方式)，P2(商品代码，供应商，库存量)","answer":0,"chooseValue":"B"},{"id":"794931212840882177","questionId":"794931210924085249","content":"P1(商品代码，商品名称，联系方式)，P2(供应商，库存量)","answer":0,"chooseValue":"C"},{"id":"794931212861853697","questionId":"794931210924085249","content":"P1(商品代码，商品名称)，P2(商品代码，供应商，库存量)，P3(供应商，联系方式)","answer":1,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931144842825729","title":"<p><strong>请作答第<span style=\"color: red\">2</span>空。</strong></p><p><br/></p><p> </p><p><br/></p><p><br/></p><p>关系R、S如下图所示，关系代数表达式π3,4,5(σ1＜6(R×S)= （1） ，对关系R、S进行自然连接后的属性列数和元组个数分别为（2）。</p><p><img style=\"max-width:100%;height:auto\" title=\"079474f420e87cca38cee47ba4ac5a2f.png\" alt=\"image.png\" src=\"https://image.chaiding.com/ruankao/079474f420e87cca38cee47ba4ac5a2f.png?x-oss-process=style/ruankaodaren\"/></p><br/>","analyze":"<p>R×S后的结果如表7.6所示。<br/></p><p><img style=\"max-width:100%;height:auto\" title=\"551abc158791ac6651a88311f6441edc.png\" alt=\"image.png\" src=\"https://image.chaiding.com/ruankao/551abc158791ac6651a88311f6441edc.png?x-oss-process=style/ruankaodaren\"/><br/></p><p>其中σ1＜6(R×S)表示选择R.A小于S.C的元组，结果如下表所示。</p><p><br/></p><p><img style=\"max-width:100%;height:auto\" title=\"3509550525ec560854999015ffd7b3e3.png\" alt=\"image.png\" src=\"https://image.chaiding.com/ruankao/3509550525ec560854999015ffd7b3e3.png?x-oss-process=style/ruankaodaren\"/><br/></p><p>将上述结果的3、4、5列进行投影</p><p><img style=\"max-width:100%;height:auto\" title=\"4d28e9a4d342483a74e54141b1e22907.png\" alt=\"image.png\" src=\"https://image.chaiding.com/ruankao/4d28e9a4d342483a74e54141b1e22907.png?x-oss-process=style/ruankaodaren\"/><br/></p><p>按选项要求整理后结果：</p><p><img style=\"max-width:100%;height:auto\" title=\"7f014c6005e3db466d4f35e0cd329970.png\" alt=\"image.png\" src=\"https://image.chaiding.com/ruankao/7f014c6005e3db466d4f35e0cd329970.png?x-oss-process=style/ruankaodaren\"/> <br/></p><p><br/></p><p><br/></p>","multi":0,"questionType":1,"answer":"A","chooseItem":["794931146692513793"],"itemList":[{"id":"794931146692513793","questionId":"794931144842825729","content":"3和0","answer":1,"chooseValue":"A"},{"id":"794931146705096705","questionId":"794931144842825729","content":"3和2","answer":0,"chooseValue":"B"},{"id":"794931146717679617","questionId":"794931144842825729","content":"6和0","answer":0,"chooseValue":"C"},{"id":"794931146734456833","questionId":"794931144842825729","content":"6和2","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931274430042113","title":"<p><strong>请作答第<span style=\"color: red\">2</span>空。</strong></p><p>分布式数据库系统除了包含集中式数据库系统的模式结构之外，还增加了几个模式级别，其中 () 定义分布式数据库中数据的整体逻辑结构，使得数据使用方便，如同没有分布一样。（）是指用户或应用程序无需知道局部使用的是哪种数据模型。</p>","analyze":"<p>本题考查分布式数据库的基本概念。</p><p>分布式数据库在各结点上独立，在全局上统一。因此需要定义全局的逻辑结构，称之为全局概念模式，全局外模式是全局概念模式的子集，分片模式和分布模式分别描述数据在逻辑上的分片方式和在物理上各结点的分布形式。</p><p>物理位置，即位置透明性，要会联想记忆。</p><p>分片透明性：用户或应用程序不需要知道逻辑上访问的表具体是如何分块存储的。</p><p>位置透明性：应用程序不关心数据存储物理位置的改变。</p><p>逻辑透明性：用户或应用程序无需知道局部使用的是哪种数据模型</p>","multi":0,"questionType":1,"answer":"B","chooseItem":["794931276422336513"],"itemList":[{"id":"794931276401364993","questionId":"794931274430042113","content":"分片透明","answer":0,"chooseValue":"A"},{"id":"794931276422336513","questionId":"794931274430042113","content":"逻辑透明","answer":1,"chooseValue":"B"},{"id":"794931276451696641","questionId":"794931274430042113","content":"位置透明","answer":0,"chooseValue":"C"},{"id":"794931276476862465","questionId":"794931274430042113","content":"复制透明","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931202439008257","title":"<p><strong>请作答第<span style=\"color: red\">2</span>空。</strong></p><p>分布式数据库系统除了包含集中式数据库系统的模式结构之外，还增加了几个模式级别，其中 (41) 定义分布式数据库中数据的整体逻辑结构，使得数据使用方便，如同没有分布一样。（42）是指用户或应用程序无需知道局部使用的是哪种数据模型。</p>","analyze":"<p>本题考查分布式数据库的基本概念。</p><p>分布式数据库在各结点上独立，在全局上统一。因此需要定义全局的逻辑结构，称之为全局概念模式，全局外模式是全局概念模式的子集，分片模式和分布模式分别描述数据在逻辑上的分片方式和在物理上各结点的分布形式。</p><p>物理位置，即位置透明性，要会联想记忆。</p><p>分片透明性：用户或应用程序不需要知道逻辑上访问的表具体是如何分块存储的。</p><p>位置透明性：应用程序不关心数据存储物理位置的改变。</p><p>逻辑透明性：用户或应用程序无需知道局部使用的是哪种数据模型。</p><p>复制透明性：用户或应用程序不关心复制的数据从何而来。</p>","multi":0,"questionType":1,"answer":"B","chooseItem":["794931204305473537"],"itemList":[{"id":"794931204292890625","questionId":"794931202439008257","content":"名片透明","answer":0,"chooseValue":"A"},{"id":"794931204305473537","questionId":"794931202439008257","content":"逻辑透明","answer":1,"chooseValue":"B"},{"id":"794931204322250753","questionId":"794931202439008257","content":"位置透明","answer":0,"chooseValue":"C"},{"id":"794931204343222273","questionId":"794931202439008257","content":"复制透明","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931193966514177","title":"<p><strong>请作答第<span style=\"color: red\">2</span>空。</strong></p>设有职工实体 Employee （职工号，姓名，性别，年龄，通信地址，家庭成员），其中通信地址记录了邮编、省、市、街道信息;家庭成员记录了职工的亲属的姓名。职工实体中的通信地址是一个（23）属性;为了将数据库模式设计的更合理，对于家庭成员属性（24）。","analyze":"本题职工实体集Employee的通信地址可以进一步分为邮编、省、市、街道。属于符合属性。为了将数据库模式设计的更合理，对于家庭成员属性应该将职工亲属的姓名加上职工号设计成为一个独立的实体。否则会职工实体有数据冗余等问题的产生。","multi":0,"questionType":1,"answer":"D","chooseItem":["794931195874922497"],"itemList":[{"id":"794931195820396545","questionId":"794931193966514177","content":"可以不作任何处理直接记录亲属的姓名","answer":0,"chooseValue":"A"},{"id":"794931195837173761","questionId":"794931193966514177","content":"只允许记录一个亲属的姓名","answer":0,"chooseValue":"B"},{"id":"794931195853950977","questionId":"794931193966514177","content":"需要对职工实体设置若干个亲属姓名字段","answer":0,"chooseValue":"C"},{"id":"794931195874922497","questionId":"794931193966514177","content":"应该将职工的亲属的姓名加上职工号设计成为一个独立的实体","answer":1,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931156100337665","title":"<p><strong>请作答第<span style=\"color: red\">2</span>空。</strong></p><p>某公司的商品(商品号，商品名称，生产商，单价)和仓库(仓库号，地址，电话，商品号，库存量)两个实体之间的关系如表1和表2所示。</p><p><img style=\"max-width:100%;height:auto\" src=\"https://image.chaiding.com/ruankao/19112328b1daaebc7e98e51484404353.jpg?x-oss-process=style/ruankaodaren\" title=\"19112328b1daaebc7e98e51484404353.jpg\" alt=\"1.jpg\"/></p><p>商品关系的主键是 （34）；仓库关系的主键是（35）；仓库关系 （36） ，为了解决这一问题，需要将仓库关系分解为 （37） 。<br/></p>","analyze":"商品关系的主键是商品号，仓库关系的主键是(仓库号，商品号)。显然，仓库关系存在冗余、修改操作的不一致，以及插入异常和删除异常。例如，仓库号为“01”的商品有3种，其地址就要重复3次，故存在冗余。为了解决仓库关系模式存在的问题，就需要进行模式分解，其中（37）空选项A存在非主属性对主键的部分函数依赖，即“仓库号→电话”。选项B存在的问题是分解属于有损联接，即分解的新关系模式仓库1和仓库2无法恢复到原关系。选项C分解存在的问题与A类同。","multi":0,"questionType":1,"answer":"C","chooseItem":["794931158042300417"],"itemList":[{"id":"794931157996163073","questionId":"794931156100337665","content":"仓库号，地址","answer":0,"chooseValue":"A"},{"id":"794931158021328897","questionId":"794931156100337665","content":"仓库号，电话","answer":0,"chooseValue":"B"},{"id":"794931158042300417","questionId":"794931156100337665","content":"仓库号，商品号","answer":1,"chooseValue":"C"},{"id":"794931158063271937","questionId":"794931156100337665","content":"地址，电话","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931167865360385","title":"<p><strong>请作答第<span style=\"color: red\">2</span>空。</strong></p><p>建立一个供应商、零件数据库。其中“供应商”表S(Sno，Sname，Zip，City)中的元素分别表示供应商代码、供应商名、供应商邮编、供应商所在城市，其函数依赖为：Sno→(Sname，Zip，City)，Zip→City。</p><p>a. “供应商”表S属于（38）。</p><p>b.若要求：供应商代码不能为空，且值是唯一的，供应商的名也是唯一的：零件号不能为空，且值是唯—的；一个供应商可以供应多种零件，而一种零件可以由多个供应商供应。请将下面的SQL语句空缺部分补充完整。</p><p>CREATE TABLE S(Sno CHAR(5) (39),</p><p>Sname CHAR(30) UNIQUE,</p><p>Zip CHAR(8),</p><p>City CHAR(20),</p><p>（40）;</p>","analyze":"<p>"供应商"表S属于2NF，因为表S的主键是Sno，非主属性Sname，Zip，City不存在对主键的部分函数依赖。但是，当2NF消除了非主属性对主键的传递函数依赖，则称为3NF。"供应商"表S不属于 3NF，因为存在传递依赖，即Sno→ Zip，Zip →City。所以正确的答案是B。</p><p>要求供应商代码不能为空，且值是唯一的，供应商的名也是唯一的，所以需要用NOT NULL UNIQUE。试题（44）正确的答案是C，因为表S的主键是Sno，所以需要用PRIMARY KEY（Sno）来约束。补充完整的SQL语句如下∶</p><p>CREATE TABLE S (Sno CHAR (5)NOT NULL UNIQUE,</p><p>Sname CHAR (30) UNIQUE,</p><p>ZIP CHAR(8),</p><p>City CHAR(20)</p><p>PRIMARY KEY(Sno));</p>","multi":0,"questionType":1,"answer":"B","chooseItem":["794931169756991489"],"itemList":[{"id":"794931169736019969","questionId":"794931167865360385","content":"FOREIGN KEY","answer":0,"chooseValue":"A"},{"id":"794931169756991489","questionId":"794931167865360385","content":"NOT NULL UNIQUE","answer":1,"chooseValue":"B"},{"id":"794931169777963009","questionId":"794931167865360385","content":"FOREIGNKEY（Sno）","answer":0,"chooseValue":"C"},{"id":"794931169794740225","questionId":"794931167865360385","content":"PRIMARY KEY（Sname）","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931259418628097","title":"<p><strong>请作答第<span style=\"color: red\">2</span>空。</strong></p><p>若要将部门表Demp中name列的查询权限赋予用户XiaoLi。并允许XiaoLi将该限授予他人。实现的SQL语句如下：</p><p>GRANT （18） ON TABLE Demp TO XiaoLi （19） 。</p>","analyze":"<p>授权语句GRANT的格式为：</p><p>GRANT <权限> [，<权限>]…</p><p>[ON <对象类型><对象名>]</p><p>TO <用户>[，<用户>]…</p><p>[WITH GRANT OPTION]；</p><p>WITH GRANT OPTION的作用是权限传递，既允许用户将其权限分配给其他用户。所以（45）空为WITH GRANT OPTION。</p><p>由于题目要求传递的权限是name列的查询权限，所以空（18）为SELECT （name）。</p>","multi":0,"questionType":1,"answer":"C","chooseItem":["794931261352202241"],"itemList":[{"id":"794931261318647809","questionId":"794931259418628097","content":"WITH FULL OPTION","answer":0,"chooseValue":"A"},{"id":"794931261335425025","questionId":"794931259418628097","content":"CASCADE","answer":0,"chooseValue":"B"},{"id":"794931261352202241","questionId":"794931259418628097","content":"WITH GRANT OPTION","answer":1,"chooseValue":"C"},{"id":"794931261368979457","questionId":"794931259418628097","content":"WITH CHECK OPTION","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931139226652673","title":"<p><strong>请作答第<span style=\"color: red\">2</span>空。</strong></p><p>假设员工关系EMP(员工号，姓名，性别，部门，部门电话，部门负责人，家庭住址，家庭成员，成员关系)如下表所示。如果一个部门只能有一部电话和一位负责人，一个员工可以有多个家庭成员，那么关系EMP属于（1），且（2）问题；为了解决这一问题，应该将员工关系EMP分解为 （3）。</p><p><img style=\"max-width:100%;height:auto\" src=\"https://image.chaiding.com/ruankao/5683ec8aab542cfd66536e2454e3583e.jpg?x-oss-process=style/ruankaodaren\" title=\"5683ec8aab542cfd66536e2454e3583e.jpg\" alt=\"1.jpg\"/></p><br/>","analyze":"本题 存在存在冗余、修改操作的不一致，以及插入异常和删除异常。","multi":0,"questionType":1,"answer":"D","chooseItem":["794931141122478081"],"itemList":[{"id":"794931141080535041","questionId":"794931139226652673","content":"无冗余、无插入异常和删除异常","answer":0,"chooseValue":"A"},{"id":"794931141093117953","questionId":"794931139226652673","content":"无冗余，但存在插入异常和删除异常","answer":0,"chooseValue":"B"},{"id":"794931141109895169","questionId":"794931139226652673","content":"存在冗余，但不存在修改操作的不一致","answer":0,"chooseValue":"C"},{"id":"794931141122478081","questionId":"794931139226652673","content":"存在冗余、修改操作的不一致，以及插入异常和删除异常","answer":1,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931216619950081","title":"<p><strong>请作答第<span style=\"color: red\">2</span>空。</strong></p><p>设ρ={（A1，A2），（A1，A3）}是关系R（A1,A2,A3）上的一个分解，下表是R上的一个关系实例r，R的函数依赖集为（ ），分解ρ（ ）。</p><img style=\"max-width:100%;height:auto\" src=\"https://image.chaiding.com/ruankao/e1f95518f8403d31d65fdc376ce621db.jpg?x-oss-process=style/ruankaodaren\" title=\"e1f95518f8403d31d65fdc376ce621db.jpg\" alt=\"1.jpg\"/>","analyze":"A1A3可以唯一确定一个A2，例如，A1=a，A3=d，可以确定A2=a。同理A1A2也能唯一确定一个A3。U1∩U2=A1，A1无法推出A2、A3，所以属于有损连接。该分解也不保持函数依赖具体可参考51CTO相关视频课程。","multi":0,"questionType":1,"answer":"C","chooseItem":["794931218494803969"],"itemList":[{"id":"794931218461249537","questionId":"794931216619950081","content":"是无损联接的","answer":0,"chooseValue":"A"},{"id":"794931218478026753","questionId":"794931216619950081","content":"是保持函数依赖的","answer":0,"chooseValue":"B"},{"id":"794931218494803969","questionId":"794931216619950081","content":"是有损联接的","answer":1,"chooseValue":"C"},{"id":"794931218507386881","questionId":"794931216619950081","content":"是否保持函数依赖是无法确定的","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931182478315521","title":"<p><strong>请作答第<span style=\"color: red\">2</span>空。</strong></p><p>设有员工实体Employee （employeelD，name，sex，birth，age，tel，departID），其中employeelD为员工号，name为员工姓名，sex为员工性别，age为员工年龄，birth为员工出生日期，tel为员工电话，记录该员的手机号码、办公室电话等，deparlD为员工所在部门号，参照另一部门实体Department的主键departID。Employee实体中存在派生属性（19）。Employee实体中还存在多值属性（20）。对属性 departID的约束是（21）。</p>","analyze":"派生属性是指可以由其他属性经过运算得到的属性，因而派生属性产生冗余，通常不存储，如本题的age;多值属性是指一个实体在该属性上会同时取多个属性，这些值也都必须存储，如本题的tel。数据约束也是描述用户信息的，根据参照完整性约束的定义，Employee实体中的departID属性应为外键。","multi":0,"questionType":1,"answer":"C","chooseItem":["794931184424472577"],"itemList":[{"id":"794931184395112449","questionId":"794931182478315521","content":"name，可以用employeelD可以区别","answer":0,"chooseValue":"A"},{"id":"794931184411889665","questionId":"794931182478315521","content":"sex，可以不作任何处理","answer":0,"chooseValue":"B"},{"id":"794931184424472577","questionId":"794931182478315521","content":"tel，可以将tel加上employeeIlD独立为一个实体","answer":1,"chooseValue":"C"},{"id":"794931184441249793","questionId":"794931182478315521","content":"tel，可以强制只记录一个电话号码","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931247812988929","title":"<p><strong>请作答第<span style=\"color: red\">2</span>空。</strong></p><p>给定关系模式R(U,F)，U={A1,A2,A3,A4}，F={A1A2→A3，A3→A4}，那么在关系R中 （15 ） 。以下说法错误的是 （16） 。</p>","analyze":"<p>由于A1A2→A3，A3→A4，根据传递性，A1A2→A4。而A1或者A2都不能推出A3或者A4。所以关系R有1个候选关键字A1A2。</p><p>由“A1A2→A3”，得不到“A1→A2A3”</p>","multi":0,"questionType":1,"answer":"A","chooseItem":["794931249666871297"],"itemList":[{"id":"794931249666871297","questionId":"794931247812988929","content":"已知F中“A1A2→A3”，可以得出“A1→A2A3”","answer":1,"chooseValue":"A"},{"id":"794931249683648513","questionId":"794931247812988929","content":"已知F中“A1A2→A3”，可以得出“A1A3→A3”","answer":0,"chooseValue":"B"},{"id":"794931249700425729","questionId":"794931247812988929","content":"已知F中“A3→A4”，可以得出“A2A3→A2A4”","answer":0,"chooseValue":"C"},{"id":"794931249717202945","questionId":"794931247812988929","content":"已知F中“A1A2→A3，A3→A4”，可以得出“A1A2→A3A4”","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931170725875713","title":"<p><strong>请作答第<span style=\"color: red\">3</span>空。</strong></p><p>建立一个供应商、零件数据库。其中“供应商”表S(Sno，Sname，Zip，City)中的元素分别表示供应商代码、供应商名、供应商邮编、供应商所在城市，其函数依赖为：Sno→(Sname，Zip，City)，Zip→City。</p><p>a. “供应商”表S属于（38）。</p><p>b.若要求：供应商代码不能为空，且值是唯一的，供应商的名也是唯一的：零件号不能为空，且值是唯—的；一个供应商可以供应多种零件，而一种零件可以由多个供应商供应。请将下面的SQL语句空缺部分补充完整。</p><p>CREATE TABLE S(Sno CHAR(5) (39),</p><p>Sname CHAR(30) UNIQUE,</p><p>Zip CHAR(8),</p><p>City CHAR(20),</p><p>（40）;</p>","analyze":"<p>"供应商"表S属于2NF，因为表S的主键是Sno，非主属性Sname，Zip，City不存在对主键的部分函数依赖。但是，当2NF消除了非主属性对主键的传递函数依赖，则称为3NF。"供应商"表S不属于 3NF，因为存在传递依赖，即Sno→ Zip，Zip →City。所以正确的答案是B。</p><p>要求供应商代码不能为空，且值是唯一的，供应商的名也是唯一的，所以需要用NOT NULL UNIQUE。试题（44）正确的答案是C，因为表S的主键是Sno，所以需要用PRIMARY KEY（Sno）来约束。补充完整的SQL语句如下∶</p><p>CREATE TABLE S (Sno CHAR (5)NOT NULL UNIQUE,</p><p>Sname CHAR (30) UNIQUE,</p><p>ZIP CHAR(8),</p><p>City CHAR(20)</p><p>PRIMARY KEY(Sno));</p>","multi":0,"questionType":1,"answer":"C","chooseItem":["794931172693004289"],"itemList":[{"id":"794931172617506817","questionId":"794931170725875713","content":"NOT NULL","answer":0,"chooseValue":"A"},{"id":"794931172655255553","questionId":"794931170725875713","content":"NOT NULL UNIQUE","answer":0,"chooseValue":"B"},{"id":"794931172693004289","questionId":"794931170725875713","content":"PRIMARY KEY(Sno)","answer":1,"chooseValue":"C"},{"id":"794931172726558721","questionId":"794931170725875713","content":"PRIMARY KEY(Sname)","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931185410134017","title":"<p><strong>请作答第<span style=\"color: red\">3</span>空。</strong></p><p>设有员工实体Employee （employeelD，name，sex，birth，age，tel，departID），其中employeelD为员工号，name为员工姓名，sex为员工性别，age为员工年龄，birth为员工出生日期，tel为员工电话，记录该员的手机号码、办公室电话等，deparlD为员工所在部门号，参照另一部门实体Department的主键departID。Employee实体中存在派生属性（19）。Employee实体中还存在多值属性（20）。对属性 departID的约束是（21）。</p>","analyze":"派生属性是指可以由其他属性经过运算得到的属性，因而派生属性产生冗余，通常不存储，如本题的age;多值属性是指一个实体在该属性上会同时取多个属性，这些值也都必须存储，如本题的tel。数据约束也是描述用户信息的，根据参照完整性约束的定义，Employee实体中的departID属性应为外键。","multi":0,"questionType":1,"answer":"C","chooseItem":["794931187331125249"],"itemList":[{"id":"794931187293376513","questionId":"794931185410134017","content":"Primary Key,NOT NULL","answer":0,"chooseValue":"A"},{"id":"794931187314348033","questionId":"794931185410134017","content":"Primary Key","answer":0,"chooseValue":"B"},{"id":"794931187331125249","questionId":"794931185410134017","content":"Foreign Key","answer":1,"chooseValue":"C"},{"id":"794931187352096769","questionId":"794931185410134017","content":"Candidate Key","answer":0,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931158973435905","title":"<p><strong>请作答第<span style=\"color: red\">3</span>空。</strong></p><p>某公司的商品(商品号，商品名称，生产商，单价)和仓库(仓库号，地址，电话，商品号，库存量)两个实体之间的关系如表1和表2所示。</p><p><img style=\"max-width:100%;height:auto\" src=\"https://image.chaiding.com/ruankao/19112328b1daaebc7e98e51484404353.jpg?x-oss-process=style/ruankaodaren\" title=\"19112328b1daaebc7e98e51484404353.jpg\" alt=\"1.jpg\"/></p><p>商品关系的主键是 （34）；仓库关系的主键是（35）；仓库关系 （36） ，为了解决这一问题，需要将仓库关系分解为 （37） 。<br/></p>","analyze":"商品关系的主键是商品号，仓库关系的主键是(仓库号，商品号)。显然，仓库关系存在冗余、修改操作的不一致，以及插入异常和删除异常。例如，仓库号为“01”的商品有3种，其地址就要重复3次，故存在冗余。为了解决仓库关系模式存在的问题，就需要进行模式分解，其中（37）空选项A存在非主属性对主键的部分函数依赖，即“仓库号→电话”。选项B存在的问题是分解属于有损联接，即分解的新关系模式仓库1和仓库2无法恢复到原关系。选项C分解存在的问题与A类同。","multi":0,"questionType":1,"answer":"D","chooseItem":["794931161049616385"],"itemList":[{"id":"794931160936370177","questionId":"794931158973435905","content":"无冗余、无插入异常，但存在删除异常","answer":0,"chooseValue":"A"},{"id":"794931160978313217","questionId":"794931158973435905","content":"无冗余，但存在插入异常和删除异常","answer":0,"chooseValue":"B"},{"id":"794931161016061953","questionId":"794931158973435905","content":"存在冗余，但不存在修改操作的不一致","answer":0,"chooseValue":"C"},{"id":"794931161049616385","questionId":"794931158973435905","content":"存在冗余、修改操作的不一致，以及插入异常和删除异常","answer":1,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931162077220865","title":"<p><strong>请作答第<span style=\"color: red\">4</span>空。</strong></p><p>某公司的商品(商品号，商品名称，生产商，单价)和仓库(仓库号，地址，电话，商品号，库存量)两个实体之间的关系如表1和表2所示。</p><p><img style=\"max-width:100%;height:auto\" src=\"https://image.chaiding.com/ruankao/19112328b1daaebc7e98e51484404353.jpg?x-oss-process=style/ruankaodaren\" title=\"19112328b1daaebc7e98e51484404353.jpg\" alt=\"1.jpg\"/></p><p>商品关系的主键是 （34）；仓库关系的主键是（35）；仓库关系 （36） ，为了解决这一问题，需要将仓库关系分解为 （37） 。<br/></p>","analyze":"商品关系的主键是商品号，仓库关系的主键是(仓库号，商品号)。显然，仓库关系存在冗余、修改操作的不一致，以及插入异常和删除异常。例如，仓库号为“01”的商品有3种，其地址就要重复3次，故存在冗余。为了解决仓库关系模式存在的问题，就需要进行模式分解，其中（37）空选项A存在非主属性对主键的部分函数依赖，即“仓库号→电话”。选项B存在的问题是分解属于有损联接，即分解的新关系模式仓库1和仓库2无法恢复到原关系。选项C分解存在的问题与A类同。","multi":0,"questionType":1,"answer":"D","chooseItem":["794931164065320961"],"itemList":[{"id":"794931163994017793","questionId":"794931162077220865","content":"仓库1(仓库号，地址)和仓库2(仓库号，电话，商品号，库存量)","answer":0,"chooseValue":"A"},{"id":"794931164019183617","questionId":"794931162077220865","content":"仓库1(仓库号，地址，电话)和仓库2(商品号，库存量)","answer":0,"chooseValue":"B"},{"id":"794931164044349441","questionId":"794931162077220865","content":"仓库1(仓库号，电话)和仓库2(仓库号，地址，商品号，库存量)","answer":0,"chooseValue":"C"},{"id":"794931164065320961","questionId":"794931162077220865","content":"仓库1(仓库号，地址，电话)和仓库2(仓库号，商品号，库存量)","answer":1,"chooseValue":"D"}],"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794918567597330433","title":"<br><p></p><h3 style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;text-indent:23.7000pt;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><span style=\"mso-spacerun:'yes';font-family:汉仪中圆简;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:12.0000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:汉仪中圆简\">试题二（</span>25<span style=\"font-family:汉仪中圆简\">分）</span></span><span style=\"mso-spacerun:'yes';font-family:汉仪中圆简;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:12.0000pt;mso-font-kerning:1.0000pt;\"></span></h3><p></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;text-indent:21.0000pt;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">阅读以下关于系统数据分析与建模的叙述，在答题纸上回答问题</span>1 <span style=\"font-family:宋体\">至问题 </span><span style=\"font-family:Times New Roman\">3</span><span style=\"font-family:宋体\">。</span></span><span style=\"mso-spacerun:'yes';font-family:'Times New Roman';mso-fareast-font-family:宋体;font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;text-indent:21.0000pt;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\">【说明】</span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;text-indent:21.0000pt;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">某软件公司受快递公司委托，拟开发一套快递业务综合管理系统，实现快递单和物流信息的综合管理。项目组在系统逻辑数据模型设计中，需要描述的快递单样式如图</span> 2-1 <span style=\"font-family:宋体\">所示，图 </span><span style=\"font-family:Times New Roman\">2-2 </span><span style=\"font-family:宋体\">是项目组针对该快递单所设计的候选实体及其属性。</span></span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;text-indent:21.0000pt;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\"><img style=\"max-width:100%;height:auto\" src=\"https://image.chaiding.com/ruankao/ec6caa69fafd6c0e183acd77bfcd6ea1.png?x-oss-process=style/ruankaodaren\"/></span></span></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;text-indent:21.0000pt;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\"><img style=\"max-width:100%;height:auto\" src=\"https://image.chaiding.com/ruankao/ffd5a4a2b46aad239faf6c8189aa23e4.png?x-oss-process=style/ruankaodaren\"/></span></span></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;text-indent:21.0000pt;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><span style=\"font-family:宋体\">【问题</span><span style=\"font-family: 宋体; font-size: 10.5pt; text-indent: 21pt;\"> 1</span><span style=\"font-family:宋体\">】（</span><span style=\"font-family:Times New Roman\">6 </span><span style=\"font-family:宋体\">分）</span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\"><br/></span></span></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;text-indent:21.0000pt;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">数据库设计主要包括概念设计、逻辑设计和物理设计三个阶段，请用</span> 200 <span style=\"font-family:宋体\">字以内文字说明这三个阶段的主要任务。</span></span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;text-indent:21.0000pt;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><strong><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">【问题</span> 2<span style=\"font-family:宋体\">】</span><span style=\"font-family:Times New Roman\">]</span><span style=\"font-family:宋体\">（</span><span style=\"font-family:Times New Roman\">11 </span><span style=\"font-family:宋体\">分）</span></span></strong><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\"><br/></span></span></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;text-indent:21.0000pt;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">根据快递单样式图，请说明</span>:</span><span style=\"mso-spacerun:'yes';font-family:'Times New Roman';mso-fareast-font-family:宋体;font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;text-indent:21.0000pt;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\">1) <span style=\"font-family:宋体\">图 </span><span style=\"font-family:Times New Roman\">2-2 </span><span style=\"font-family:宋体\">中三个候选实体对应的主属性 </span><span style=\"font-family:Times New Roman\">PK1</span><span style=\"font-family:宋体\">、</span><span style=\"font-family:Times New Roman\">PK2 </span><span style=\"font-family:宋体\">和 </span><span style=\"font-family:Times New Roman\">PK3 </span><span style=\"font-family:宋体\">分别是什么</span><span style=\"font-family:Times New Roman\">?</span></span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;text-indent:21.0000pt;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\">2) <span style=\"font-family:宋体\">图 </span><span style=\"font-family:Times New Roman\">2-2 </span><span style=\"font-family:宋体\">中应设计哪些实体之间的联系，并说明联系的类型。</span></span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;text-indent:21.0000pt;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\"></span></span><strong><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">【问题</span> 3<span style=\"font-family:宋体\">】（</span><span style=\"font-family:Times New Roman\">8 </span><span style=\"font-family:宋体\">分）</span></span></strong><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\"><br/></span></span></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;text-indent:21.0000pt;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">在图</span> 2-2 <span style=\"font-family:宋体\">中添加实体之间的联系后，该实体联系图是否满足第一范式、第二范式和第三范式中的要求（对于每种范式判定时，假定己满足低级别范式要求</span><span style=\"font-family:Times New Roman\">)</span><span style=\"font-family:宋体\">。如果不满足，请用 </span><span style=\"font-family:Times New Roman\">200 </span><span style=\"font-family:宋体\">字以内文字分别说明其原因。</span></span><span style=\"mso-spacerun:'yes';font-family:'Times New Roman';mso-fareast-font-family:宋体;font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p>","analyze":"<p><span style=\"font-family:宋体\">【问题</span><span style=\"font-family: 宋体; font-size: 10.5pt; text-indent: 21pt;\"> 1</span><span style=\"font-family:宋体\">】（</span><span style=\"font-family:Times New Roman\">6 </span><span style=\"font-family:宋体\">分）</span></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;text-indent:21.0000pt;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;background:#D9D9D9;mso-shading:#D9D9D9;\"><span style=\"font-family:宋体\">答案</span></span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\">：</span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;text-indent:21.0000pt;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">概念设计也称为概念结构设计，其任务是在需求分析阶段产生的需求说明书的基础上，按照特定的方法将它们抽象为一个不依赖于任何</span> DBMS <span style=\"font-family:宋体\">的数据模型，即概念模型。概念模型的表现形式即 </span><span style=\"font-family:Times New Roman\">ER </span><span style=\"font-family:宋体\">模型。</span></span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;text-indent:21.0000pt;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">逻辑设计也称为逻辑结构设计，其主要任务是将概念模型转换为某个特定的</span> DBMS <span style=\"font-family:宋体\">上的逻辑模型。设计逻辑结构时，首先为概念模型选定一个合适的逻辑模型（如：关系模式或层次模型），然后将其转化为由特定 </span><span style=\"font-family:Times New Roman\">DBMS </span><span style=\"font-family:宋体\">支持的逻辑模型，最后对逻辑模型进行优化。物理设计也称为物理结构设计，其任务是对给定的逻辑模型选取一个最适合应用环境的物理结构，所谓数据库的物理结构，主要是指数据库在物理设备上的存储结构和存取方法。</span></span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span><span style=\"mso-spacerun:'yes';font-family:'Times New Roman';mso-fareast-font-family:宋体;color:#FF0000;font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><strong><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">【问题</span> 2<span style=\"font-family:宋体\">】</span><span style=\"font-family:Times New Roman\">]</span><span style=\"font-family:宋体\">（</span><span style=\"font-family:Times New Roman\">11 </span><span style=\"font-family:宋体\">分）</span></span></strong></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;text-indent:21.0000pt;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;background:#D9D9D9;mso-shading:#D9D9D9;\"><span style=\"font-family:宋体\">答案</span></span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\">：</span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;text-indent:21.0000pt;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\">（</span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\">1</span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\">）</span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"> </span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\">PK1<span style=\"font-family:宋体\">：证件号</span></span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\">；</span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\">PK2<span style=\"font-family:宋体\">：编号</span></span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\">；</span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\">PK3<span style=\"font-family:宋体\">：证件号</span></span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;text-indent:21.0000pt;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\">（</span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\">2</span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\">）</span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"> </span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">联系</span>1<span style=\"font-family:宋体\">：寄件人与快递单之间应有联系，联系类型：</span><span style=\"font-family:Times New Roman\">1:N</span><span style=\"font-family:宋体\">。</span></span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;text-indent:51.7500pt;mso-char-indent-count:5.0000;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">联系</span>2<span style=\"font-family:宋体\">：收件人与快递单之间应有联系，联系类型：</span><span style=\"font-family:Times New Roman\">1:N</span><span style=\"font-family:宋体\">。</span></span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><strong><span style=\"font-family: 宋体; font-size: 10.5pt;\"><span style=\"font-family:宋体\">【问题</span> 3<span style=\"font-family:宋体\">】（</span><span style=\"font-family:Times New Roman\">8 </span><span style=\"font-family:宋体\">分）</span></span></strong></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;text-indent:21.0000pt;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;background:#D9D9D9;mso-shading:#D9D9D9;\"><span style=\"font-family:宋体\">答案</span></span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\">：</span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\">寄件人</span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\">和</span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">收件人满足第</span>3<span style=\"font-family:宋体\">范式，因为这两个关系消除了部分函数依赖与传递函数依赖。快递单满足第</span><span style=\"font-family:Times New Roman\">2</span><span style=\"font-family:宋体\">范式，但不满足第</span><span style=\"font-family:Times New Roman\">3</span><span style=\"font-family:宋体\">范式，</span></span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\">因为</span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">总计可由前边的保价金额、代收货款、运费、加急费、包装费、保价费等计算得出，存在传递函数依赖，不满足</span>3NF<span style=\"font-family:宋体\">。</span></span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p>","multi":0,"questionType":3,"answer":"<p>见解析</p>","chooseItem":null,"itemList":null,"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794918336482791425","title":"<br><p>试题四（25分）阅读以下关于数据库设计的叙述，在答题纸上回答问题1至问题3。【说明】某航空公司要开发一个订票信息处理系统，以方便各个代理商销售机票。开发小组经过设计，给出该系统的部分关系模式如下：航班（航班编号，航空公司，起飞地，起飞时间，目的地，到达时间，剩余票数，票价）代理商（代理商编号，代理商名称，客服电话，地址，负责人）机票代理（代理商编号，航班编号，票价）旅客（身份证号，姓名，性别，出生日期，电话）购票（购票单号，身份证号，航班编号，搭乘日期，购票金额）在提供给用户的界面上，其核心功能是当用户查询某航班时，将该航班所有的代理商信息及其优惠票价信息，返回给用户，方便用户购买价格优惠的机票。在实现过程中发现，要实现此功能，需要在代理商和机票代理两个关系模式上进行连接操作，性能很差。为此开发小组将机票代理关系模式进行了扩充，结果为：机票代理（代理商编号，航班编号，代理商名称，客服电话，票价）这样，用户在查找信息时只需对机票代理关系模式进行查询即可，提高了查询效率。<br/>【问题1】（6分）机票代理关系模式的修改，满足了用户对代理商机票价格查询的需求，提高了查询效率。但这种修改导致机票代理关系模式不满足3NF，会带来存储异常的问题。<br/>1）请具体说明其问题，并举例说明。<br/></p><p>2）这种存储异常会造成数据不一致，请给出解决该存储异常的方案。</p><p>【问题2】（9分）</p><p>在机票销售信息处理系统中，两个代理商的售票并发执行，可能产生的操作序列如表4-1所示。</p><p><img style=\"max-width:100%;height:auto\" src=\"https://image.chaiding.com/ruankao/63c16f39c155fe05f42eba4f292206ab.png?x-oss-process=style/ruankaodaren\" title=\"63c16f39c155fe05f42eba4f292206ab.png\" alt=\"3.png\"/><br/><br/></p><p>假设两个代理商执行之前，该航班仅剩1张机票。</p><p>1）请说明上述两个代理商操作的结果。</p><p>2）并发操作会带来数据不一致的问题，请具体说明3种问题。</p><p>【问题3】（10分）</p><p>为了避免问题2中的问题，开发组使用库的读写锁机制，操作序列变为表4-2所示。</p><p><img style=\"max-width:100%;height:auto\" src=\"https://image.chaiding.com/ruankao/819178a77e3dc2c79123810a0a68817f.png?x-oss-process=style/ruankaodaren\" title=\"819178a77e3dc2c79123810a0a68817f.png\" alt=\"4.png\"/><br/><br/></p>","analyze":"<p>【问题1】（6分）<br/></p><p>1）请具体说明其问题，并举例说明。</p><p>【参考答案】</p><p>不满足3NF会产生函数的传递依赖，造成数据冗余和修改异常等问题。</p><p>① 数据冗余</p><p>一个代理商会代理多家航班的机票销售业务，在机票代理模式中，该代理商的代理商名称，客服电话就会被存储多次，造成数据的冗余。</p><p>② 修改异常</p><p>当需要修改该代理商的名称或客服电话时，就要修改所有相应元组中的名称或客服电话，否则就会出现客服电话值不一致的现象，产生修改异常。</p><p>2）这种存储异常会造成数据不一致，请给出解决该存储异常的方案。</p><p>【参考答案】</p><p>可使用触发器在修改时，检查并新更对应数据的方式来解决数据不一致的问题。比如可以在代理商关系模式上加触发器，当修改代理商关系模式的数据时，同步修改机票代理关系模式。<br/></p><p>【问题2】（9分）</p><p>1）请说明上述两个代理商操作的结果。</p><p>【参考答案】</p><p>两个代理商都显示剩余票数是1，但是代理商1可以正常售票，代理商2操作时系统会出错。因为票已经被代理商1 售完了。</p><p>2）并发操作会带来数据不一致的问题，请具体说明3种问题。</p><p>【参考答案】</p><p>数据库的并发操作会带来一些数据不一致问题。例如，丢失修改、读脏数据和不可重复读等。</p><p>① 丢失修改。事务A与事务B从数据库中读入同一数据并修改，事务B的提交结果破坏了事务A提交的结果，导致事务A的修改被丢失。</p><p>② 读脏数据。事务A修改某一数据，并将其写回磁盘，事务B读取同一数据后，事务A由于某种原因被撤销，从而导致事务B读到的数据是无效数据。</p><p>③ 不可重复读。事务A读取数据后，事务B又修改了该数据，但事务A使用的仍是修改之前的值。因此。事务A与事务B分别得到不同的结果，产生了数据的不一致性。<br/></p><p>【问题3】（10分）</p><p>【参考答案】</p><p>（1）加写锁</p><p>（2）加读锁</p><p>（3）加写锁</p><p>（4）被阻塞等待</p><p>（5）得到通知</p><p>（6）加写锁</p><p>采用封锁的方法虽然可以有效防止数据的不一致性，但也会产生死锁问题。死锁是指多个用户申请不同封锁，由于申请者均拥有一部分封锁权，而又需等待另外用户拥有的部分封锁而引起的永无休止的等待。</p><br/><br/><br/>","multi":0,"questionType":3,"answer":"<p>见解析</p>","chooseItem":null,"itemList":null,"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794918569472184321","title":"<br><p><br/></p><h3 style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;text-indent:23.7000pt;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><span style=\"mso-spacerun:'yes';font-family:汉仪中圆简;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:12.0000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:汉仪中圆简\">试题四</span>( 25 <span style=\"font-family:汉仪中圆简\">分）</span></span><span style=\"mso-spacerun:'yes';font-family:汉仪中圆简;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:12.0000pt;mso-font-kerning:1.0000pt;\"></span></h3><p><br/></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;text-indent:21.0000pt;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">阅读以下关于数据库分析与建模的叙述，在答题纸上回答问题</span> 1<span style=\"font-family:宋体\">至问题 </span><span style=\"font-family:Times New Roman\">3</span><span style=\"font-family:宋体\">。</span></span><span style=\"mso-spacerun:'yes';font-family:'Times New Roman';mso-fareast-font-family:宋体;font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;text-indent:21.0000pt;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\">【说明】</span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;text-indent:21.0000pt;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">某电子商务企业随着业务不断发展，销售订单不断增加，每月订单超过了</span> 50 <span style=\"font-family:宋体\">万笔，急需开发一套新的互联网电子订单系统。同时该电商希望建立相应的数据中心，能够对订单数据进行分析挖掘，以便更好地服务用户。王工负责订单系统的数据库设计与开发，初步设计的核心订单关系模式为</span><span style=\"font-family:Times New Roman\">:orders(order_no</span><span style=\"font-family:宋体\">，</span><span style=\"font-family:Times New Roman\">customer_no </span><span style=\"font-family:宋体\">，</span><span style=\"font-family:Times New Roman\">order_date</span><span style=\"font-family:宋体\">，</span><span style=\"font-family:Times New Roman\">product_no</span><span style=\"font-family:宋体\">，</span><span style=\"font-family:Times New Roman\">price</span><span style=\"font-family:宋体\">，</span><span style=\"font-family:Times New Roman\">. ....);</span></span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;text-indent:21.0000pt;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\">考虑订单数据过多，单一表的设计会对系统性能产生较大影响，仅仅采用索引不足以解决性能问题。因此，需要将订单表拆分，按月存储。</span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;text-indent:21.0000pt;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\">王工采用反规范化设计方法来解决，给出了相应的解决方案。李工负责数据中心的设计与开发。李工认为王工的解决方案存在问题，建议采用数据物理分区技术。在解决性能问题的同时，也为后续的数据迁移、数据挖掘和分析等工作提供支持。</span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;text-indent:21.0000pt;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">【问题</span> 1<span style=\"font-family:宋体\">】 </span><span style=\"font-family:Times New Roman\">(8 </span><span style=\"font-family:宋体\">分</span><span style=\"font-family:Times New Roman\">)</span></span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;text-indent:21.0000pt;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">常见的反规范化设计包括增加冗余列、增加派生列、重新组表和表分割。为解决题干所述需求，王工采用的是哪种方法</span>?<span style=\"font-family:宋体\">请用 </span><span style=\"font-family:Times New Roman\">300 </span><span style=\"font-family:宋体\">字以内的文字解释说明该方法，并指出其优缺点。</span></span></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><span style=\"font-family:宋体\">【问题</span><span style=\"font-family: 宋体; font-size: 10.5pt; text-indent: 21pt;\"> 2</span><span style=\"font-family:宋体\">】 </span><span style=\"font-family:Times New Roman\">(8 </span><span style=\"font-family:宋体\">分）</span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\"><br/></span></span></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;text-indent:21.0000pt;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">物理数据分区技术一般分为水平分区和垂直分区，数据库中常见的是水平分区。水平分区分为范围分区、哈希分区、列表分区等。请阅读下表，在</span>(1)~(8) <span style=\"font-family:宋体\">中填写不同分区方法在数据值、数据管理能力、实施难度与可维护性、数据分布等方面的特点。</span></span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;text-indent:21.0000pt;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\"><img style=\"max-width:100%;height:auto\" src=\"https://image.chaiding.com/ruankao/bfd9d8efb84ee4900216b3e7d59f1929.png?x-oss-process=style/ruankaodaren\"/></span></span></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;text-indent:21.0000pt;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><span style=\"font-family:宋体\">【问题</span><span style=\"font-family: 宋体; font-size: 10.5pt; text-indent: 21pt;\"> 3</span><span style=\"font-family:宋体\">】</span><span style=\"font-family:Times New Roman\">(9 </span><span style=\"font-family:宋体\">分）</span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\"><br/></span></span></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;text-indent:21.0000pt;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">根据需求，李工宜选择物理水平分区中的哪种分区方法</span>?<span style=\"font-family:宋体\">请用 </span><span style=\"font-family:Times New Roman\">300</span><span style=\"font-family:宋体\">字以内的文字分别解释说明该方法的优缺点。</span></span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;text-indent:21.0000pt;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\"><br/></span></span></p>","analyze":"<p><span style=\"font-family:宋体\">【问题</span><span style=\"font-family: 宋体; font-size: 10.5pt; text-indent: 21pt;\"> 1</span><span style=\"font-family:宋体\">】 </span><span style=\"font-family:Times New Roman\">(8 </span><span style=\"font-family:宋体\">分</span><span style=\"font-family:Times New Roman\">)</span></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;text-indent:21.0000pt;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;background:#D9D9D9;mso-shading:#D9D9D9;\"><span style=\"font-family:宋体\">答案</span></span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\">：</span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;text-indent:21.0000pt;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\">\t</span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">王工采用的是表分割方式中的水平分割（分割参数是：</span>“月”）</span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;text-indent:21.0000pt;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\">\t</span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\">表分割包括水平分割与垂直分割两种形式：</span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;text-indent:21.0000pt;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\">\t</span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\">水平分割：按记录进行分割，不同的记录可以分开保存，每个子表的列数相同。分割的条件可能是某列或多列数据的值，如时间参数。</span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;text-indent:21.0000pt;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\">\t</span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\">垂直分割：按进行分割，即把一条记录分开多个地方保存，每个子表的行数相同。把主键和一些行放到一个表，然后把主键和另外的列放到另一个表中，通过主键进行关联。</span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\">优点：水平分割后可以降低在查询时需要读取的数据和索引页数，同时也降低了索引的层数，提高查询速度。</span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\">缺点：水平分割会给应用增加复杂度，在查询时需要多个表名，查询所有数据需要</span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\">union<span style=\"font-family:宋体\">操作。</span></span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;text-indent:21.0000pt;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">【问题</span> 2<span style=\"font-family:宋体\">】 </span><span style=\"font-family:Times New Roman\">(8 </span><span style=\"font-family:宋体\">分）</span></span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;text-indent:21.0000pt;mso-layout-grid-align:none;text-autospace:ideograph-numeric;text-align:justify;text-justify:inter-ideograph;\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;background:#D9D9D9;mso-shading:#D9D9D9;\"><span style=\"font-family:宋体\">答案</span></span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"><span style=\"font-family:宋体\">：（</span>1<span style=\"font-family:宋体\">）连续（</span><span style=\"font-family:Times New Roman\">2</span><span style=\"font-family:宋体\">）离散（</span><span style=\"font-family:Times New Roman\">3</span><span style=\"font-family:宋体\">）弱（</span><span style=\"font-family:Times New Roman\">4</span><span style=\"font-family:宋体\">）强（</span><span style=\"font-family:Times New Roman\">5</span><span style=\"font-family:宋体\">）不好（</span><span style=\"font-family:Times New Roman\">6</span><span style=\"font-family:宋体\">）不好（</span><span style=\"font-family:Times New Roman\">7</span><span style=\"font-family:宋体\">）不均匀（</span><span style=\"font-family:Times New Roman\">8</span><span style=\"font-family:宋体\">）均匀</span></span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;text-indent:21.0000pt;mso-layout-grid-align:none;text-autospace:ideograph-numeric;text-align:justify;text-justify:inter-ideograph;\"><span style=\"font-family:宋体\">【问题</span><span style=\"font-family: 宋体; font-size: 10.5pt; text-indent: 21pt;\"> 3</span><span style=\"font-family:宋体\">】</span><span style=\"font-family:Times New Roman\">(9 </span><span style=\"font-family:宋体\">分）</span></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;text-indent:21.0000pt;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;background:#D9D9D9;mso-shading:#D9D9D9;\"><span style=\"font-family:宋体\">答案：</span></span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;background:#D9D9D9;mso-shading:#D9D9D9;\"></span></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;text-indent:21.0000pt;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\">李工宜选择范围分区方式。</span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;text-indent:21.0000pt;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\">范围分区优点：</span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;text-indent:21.0000pt;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\">1<span style=\"font-family:宋体\">、分区表可以将表存储到多个表空间内，各个分区维护各自的本地索引，查询语句可以根据索引进行分区范围查找，提高了查询速度；</span></span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;text-indent:21.0000pt;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\">2<span style=\"font-family:宋体\">、可以对单个分区进行备份、归档或者清除过期的数据，利于维护；</span></span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;text-indent:21.0000pt;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\">3<span style=\"font-family:宋体\">、实现容易，而且可以方便的对表的分区进行添加、删除、拆分和合并操作。</span></span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p><p class=\"MsoNormal\" style=\"margin-right:0.0000pt;mso-para-margin-right:0.0000gd;text-indent:21.0000pt;mso-layout-grid-align:none;text-autospace:ideograph-numeric;\"><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\">范围分区缺点：数据分布不均匀所以可以与哈希分区组合应用。</span><span style=\"mso-spacerun:'yes';font-family:宋体;mso-ascii-font-family:'Times New Roman';mso-hansi-font-family:'Times New Roman';mso-bidi-font-family:'Times New Roman';font-size:10.5000pt;mso-font-kerning:1.0000pt;\"></span></p>","multi":0,"questionType":3,"answer":"<p>见解析</p>","chooseItem":null,"itemList":null,"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null},{"id":"794931302506713089","title":"<br><p><br/></p><p><br/></p><h3>试题三（25 分)</h3><p>某集团公司在各省均设有分公司，现欲建立全国统一的销售管理信息系统，以便总公司及时掌握各分公司的销售情况。公司成立专门的项目组进行该系统的研发工作，其中张工负责其中的数据库设计工作。</p><p>张工和需求分析小组紧密合作，在设计出数据流图和数据字典的基础上，给出了数据库关系模式和相应的索引设计。同时考虑到未规范化关系模式可能引起的各类数据错误，对关系模式进行了全面的规范化处理，使所有关系模式均达到了3NF或BCNF。</p><p>在项目实施过程中，应用开发小组认为该设计方案未考虑应用功能的实际需求。如果严格按照设计方案实施，会对应用系统中整体性能产生较大影响。主要的原因在于进行数据查询时，会产生大量的多表连接操作，影响性能。而设计方案中的索引设计，并不能完全满足数据查询的性能要求。</p><p>应用开发小组还认为，该设计方案未考虑到信息系统中核心销售数据处理的特点：各分公司在使用该信息系统时只能操作自己分公司的销售数据，无权操作其它分公司的销售数据；只有总公司有权利操作所有销售数据，以便进行统计分析。</p><p>应用开发小组要求，在数据库设计方案中，必须针对实际应用功能的实现来考虑关系模式的规范化，必要时需要采用逆规范化或解除规范化的方法来保证性能要求。</p><p>【问题1】</p><p>系统需要管理供应商和货物等信息，具体包括供应商姓名、地址以及货物名称、价格等，供应商可以提供0~n种货物，其公司地址也可能发生变化。请以供应商关系模式supplier(name,address,product,price)为例，解释不规范的关系模式存在哪些问题。</p><p>【问题2】</p><p>应用开发小组认为张工的规范化设计虽然解决了未规范化关系模式带来的问题，但实际实现功能时会造成系统性能的下降，请解释其原因。</p><p>【问题3】</p><p>请解释逆规范化方法，说明其优缺点。</p><p>【问题4】</p><p>针对该信息系统中核心销售数据处理的特点，如采用关系表水平分割的逆规范化方法，请给出具体的解决方案，并说明该方案存在的问题。<span style=\"mso-spacerun:'yes';font-family:Calibri;mso-fareast-font-family:宋体;mso-bidi-font-family:'Times New Roman';font-size:12.0000pt;mso-font-kerning:0.0000pt;\"></span></p><p><br/></p>","analyze":"<p><br/></p><p><br/></p><p>一、试题分析</p><p>本题是一个数据库设计方面的考题，考查的知识点包括规范化理论和反规范化理论（逆规范化）。</p><p>规范化的基本思想是逐步消除不合适的函数依赖，使数据库中的各个关系模型达到某种程度的分离。规范化解决的主要是单个实体的质量问题，是对于问题域中原始数据展现的正规化处理。</p><p>规范化理论给出了判断关系模型优劣的理论标准，帮助预测模式可能出现的问题，是数据库逻辑设计的指南和工具，具体有：</p><p>（1）用数据依赖的概念分析和表示各数据项之间的关系。</p><p>（2）消除E-R图中的冗余联系。</p><p>若不进行规范化处理，可能产生的问题包括：数据冗余、修改异常、插入异常、删除异常。下面举例说明这些问题的具体表现形式。</p><p>设有一个关系模式R（SNAME，CNAME，TNAME TADDRESS），其属性分别表示学生姓名、选修的课程名、任课教师姓名和任课教师地址。仔细分析一下，就会发现这个模式存在下列存储异常的问题：</p><p>（1）数据冗余：如果某门课程有100个学生选修，那么在R的关系中就要出现100个元组，这门课程的任课教师姓名和地址也随之重复出现100次。</p><p>（2）修改异常：由于上述冗余问题，当需要修改这个教师的地址时，就要修改100个元组中的地址值，否则就会出现地址值不一致的现象。</p><p>（3）插入异常：如果不知道听课学生名单，这个教师的任课情况和家庭地址就无法进入数据库；否则就要在学生姓名处插入空值。</p><p>（4）删除异常：如果某门课程的任课教师要更改，那么原来任课教师的地址将随之丢失。</p><p>在本题中，也存在同样的问题：</p><p>（1）数据冗余：关系模式中多次重复记录了同一供应商的地址。</p><p>（2）插入异常：如果还未确定一个供应商有哪些货物，只是想添加一个供应商的地址信息，则会产生产品与价格均为空的记录。</p><p>（3）修改异常：当修改一个供应商的地址时，需要将多条记录同时更新，若未同时更新，则数据产生不一致。</p><p>（4）删除异常：当删除一个供应商的货物时，其地址信息被一并删除。</p><p>数据库中的数据规范化的优点是减少了数据冗余，节约了存储空间，相应逻辑和物理的I/O次数减少，同时加快了增、删、改的速度，但是对完全规范的数据库查询，通常需要更多的连接操作，从而影响查询的速度。因此，有时为了提高某些查询或应用的性能而破坏规范规则，即反规范化（非规范化处理）。</p><p>因此，题目中所说的“应用开发小组认为张工的规范化设计虽然解决了未规范化关系模式带来的问题，但实际实现功能时会造成系统性能的下降”，主要就是查询效率下降。其原因是规范化过程中对数据表进行了不断的拆分，导致一个查询需要进行多表连接，效率自然就下降了。</p><p>具体来说，常见的反规范化技术包括：</p><p>（1）增加冗余列</p><p>增加冗余列是指在多个表中具有相同的列，它常用来在查询时避免连接操作。例如：以规范化设计的理念，学生成绩表中不需要字段“姓名”，因为“姓名”字段可以通过学号查询到，但在反规范化设计中，会将“姓名”字段加入到表中。这样查询一个学生的成绩时，不需要与学生表进行连接操作，便可得到对应的“姓名”。</p><p>（2）增加派生列</p><p>增加派生列指增加的列可以通过表中其它数据计算生成。它的作用是在查询时减少计算量，从而加快查询速度。例如：订单表中，有商品号、商品单价、采购数量，我们需要订单总价时，可以通过计算得到总价，所以规范化设计的理念是无须在订单表中设计“订单总价”字段。但反规范化则不这样考虑，由于订单总价在每次查询都需要计算，这样会占用系统大量资源，所以在此表中增加派生列“订单总价”以提高查询效率。</p><p>（3）重新组表</p><p>重新组表指如果许多用户需要查看两个表连接出来的结果数据，则把这两个表重新组成一个表来减少连接而提高性能。</p><p>（4）分割表</p><p>有时对表做分割可以提高性能。表分割有两种方式：</p><p>水平分割：根据一列或多列数据的值把数据行放到两个独立的表中。水平分割通常在下面的情况下使用：</p><p>情况1：表很大，分割后可以降低在查询时需要读的数据和索引的页数，同时也降低了索引的层数，提高查询速度。</p><p>情况2：表中的数据本来就有独立性，例如表中分别记录各个地区的数据或不同时期的数据，特别是有些数据常用，而另外一些数据不常用。</p><p>情况3：需要把数据存放到多个介质上。</p><p>垂直分割：把主码和一些列放到一个表，然后把主码和另外的列放到另一个表中。如果一个表中某些列常用，而另外一些列不常用，则可以采用垂直分割，另外垂直分割可以使得数据行变小，一个数据页就能存放更多的数据，在查询时就会减少I/O次数。其缺点是需要管理冗余列，查询所有数据需要连接操作。 问题4要求提出水平分割方案，实际上就是把数据表按记录进行拆分，并存储于不同的位置。由于本题中数据的使用存在这样的特性——“各分公司在使用该信息系统时只能操作自己分公司的销售数据，无权操作其它分公司的销售数据；只有总公司有权利操作所有销售数据，以便进行统计分析”，所以按省，每个分公司存储自己的数据，这样能达到高效查询的目的，只是这样会让总公司的统计分析变得十分的低效。</p><p>二、参考答案</p><p>【问题1】</p><p>（1）数据冗余：关系模式中多次重复记录了同一供应商的地址。</p><p>（2）插入异常：如果还未确定一个供应商有哪些货物，只是想添加一个供应商的地址信息，则会产生产品与价格均为空的记录。</p><p>（3）修改异常：当修改一个供应商的地址时，需要将多条记录同时更新，若未同时更新，则数据产生不一致。</p><p>（4）删除异常：当删除一个供应商的货物时，其地址信息被一并删除。</p><p>【问题2】</p><p>数据库规范化的过程，实际是对数据表的不断拆分，以达到更高的规范程度。这样处理，带来的问题是：系统中大量查询不能通过单表完成，而需要将多表进行连接查询，所以表拆分得越多，查询性能也就越差。</p><p>【问题3】</p><p>逆规范化方法优点：提高统计、查询效率。</p><p>逆规范化方法缺点：增加了数据冗余，浪费存储空间，增、删、改操作的效率降低，可能导致数据不一致，可能产生添加、修改、删除异常。</p><p>【问题4】</p><p>解决方案：将各省的数据存放于各省分公司。</p><p>该方案主要问题在于总公司进行全国数据统计时，需要从各省服务器调取数据，效率较低。<span style=\"mso-spacerun:'yes';font-family:Calibri;mso-fareast-font-family:宋体;mso-bidi-font-family:'Times New Roman';font-size:12.0000pt;mso-font-kerning:0.0000pt;\"></span></p><p><br/></p>","multi":0,"questionType":3,"answer":"<p>见解析</p>","chooseItem":null,"itemList":null,"userAnswer":null,"userChooseItem":null,"answerCorrect":null,"userCollect":null}]}}
