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When we talk about a database, we must d
When we talk about a database, we must d
admin
2022-08-02
78
问题
When we talk about a database, we must differentiate between the database (1),which is the logical design of the database, and the database (2), which is a snapshot of the data in the database at a given instant in time. The concept of a relation corresponds to the programming-language notion of a variable, while the concept of a relation schema corresponds to the programming-language notion of type definition. In general, a relation schema consists of a list of(3)and their corresponding domains. The concept of a relation instance corresponds to the programming-language notion of a value of a (4) . The value of a given variable may change with time; similarly the contents of a relation instance may change with time as the relation is updated. In contrast, the (5) Of a relation does not generally change.问题1 A.schema B.instance C.table D.entity问题2 A.schema B.table C.instance D.entity问题3 A.variable B.attributes C.rows D.notions问题4 A.constant B.variable C.struct D.array问题5 A.table B.schema C.instance D.view
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答案
ACBBB
解析
第1空和2空:当我们谈论数据库时,我们必须区分数据库模式(它是数据库的逻辑设计)和数据库实例(它是给定时刻数据库中数据的快照)。
第3空:一般来说,关系模式由属性列表以及相应的域组成。比如R(A1,A2,…An)。
第4空:关系实例的概念对应于编程语言中变量值的概念。
第5空:类似地,关系实例的内容可能会随着时间的推移而变化,因为关系会被更新。相反,关系的模式通常不会改变。
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本试题收录于:
中级 数据库系统工程师题库软件水平考试初中高级分类
中级 数据库系统工程师
软件水平考试初中高级
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