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●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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