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The entity-relationship（E-R）data model is based on a perception of a real world that consists of a clletion of basic objects,called（请作答此空），and of relationships among these objects.An entity is a“thing”or"object"in the real world that is distinguishable from other objects.Entities are described in a database by asetof（ ）:A relationship isan association among several entities.The set of all entities of the same type and the set of all relationships of the ametype are termed an entity sct and relationship set,respectively.The overall logical structure（schema）of a database can be expressed graphically by an E-R diagram,which is built up from the fllowing components:（ ）represent entity set,（ ）represent atributes,ete.In addition to entities and relations,the E-R model represents certain（ ）to which thecontents of a database must conform.The entity-relationship model is widely used in database design.
A.data
B.things
C.entities
D.objects
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数据库系统的组成不包括（）
A.数据库
B.硬件
C.操作系统
D.人员
A.数据库
B.硬件
C.操作系统
D.人员
若in、out分别表示入队、出队操作，初始队列为空且元素a、b、c依次入队，则经过操作序列in、in、out、out、in、out之后，得到的出队序列为()。
A.cba
B.bac
C.bca
D.abc
A.cba
B.bac
C.bca
D.abc
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A.软件维护要解决软件产品交付用户之后运行中发生的各种问题
B.软件的维护期通常比开发期长得多，其投入也大得多
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A.软件维护要解决软件产品交付用户之后运行中发生的各种问题
B.软件的维护期通常比开发期长得多，其投入也大得多
C.进行质量保证审查可以提高软件产品的可维护性
D.提高可维护性是在软件维护阶段考虑的问题
授权语句GRANT中，以下关于WITHGRANTOPTION子句的叙述中，正确的是（）。
A.用于指明该授权语句将权限赋给全体用户
B.用于指明授权语句中，该用户获得的具体权限类型
C.用于指明授权语句中，获得授权的具体用户是谁
D.用于指明获得权限的用户还可以将该权限赋给其他用户
A.用于指明该授权语句将权限赋给全体用户
B.用于指明授权语句中，该用户获得的具体权限类型
C.用于指明授权语句中，获得授权的具体用户是谁
D.用于指明获得权限的用户还可以将该权限赋给其他用户
The entity-relationship（E-R）data model is based on a perception of a real world that consists of a clletion of basic objects,called（ ），and of relationships among these objects.An entity is a“thing”or"object"in the real world that is distinguishable from other objects.Entities are described in a database by asetof（请作答此空）:A relationship isan association among several entities.The set of all entities of the same type and the set of all relationships of the ametype are termed an entity sct and relationship set,respectively.The overall logical structure（schema）of a database can be expressed graphically by an E-R diagram,which is built up from the fllowing components:（ ）represent entity set,（ ）represent atributes,ete.In addition to entities and relations,the E-R model represents certain（ ）to which thecontents of a database must conform.The entity-relationship model is widely used in database design.
A.keys
B.attributes
C.records
D.Rows
A.keys
B.attributes
C.records
D.Rows