专题课程
2021年上半年数据库系统工程师上午考试已结束，今天课课家小编为大家整理了2021年上半年数据库系统工程师上午真题及答案解析(71-75)。
为方便广大考生考后估分对答案，课课家小编特向广大学员和网友搜集整理了2021年上半年数据库系统工程师真题答案，供大家参考。
●When we talk about a database, we must differentiate between the database_ (71)_ ,which is the logical design of the database, and the database_ (72) , 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 listof(73)and their corresponding domains. The concept of a relation instance corresponds to the programming-language notion of a value of a (74) . The valueof 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_ (75) оfa relation does not generally change.
(71)A.schema
B.instance
C.table
D.entity
(72)A.schema
B.table
C.instance
D.entity
(73)
A.variable
B.attributes
C.rows
D.notions
(74)A.constant
B.variable
C.struct
D.array
(75)A.table
B.schema
C.instance
D.view
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