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  3. When we talk about a database, we must d

When we talk about a database, we must d

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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
选项
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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中级 数据库系统工程师

软件水平考试初中高级

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