| 术语 | optional member |
| 释义 | optional member 可选成员 1. The specification of set membership such that the membership of a record occurrence in a set is not necessarily permanent. Its membership in a set occurrence may be changed without its being deleted from the database. Optional set membership of the record occurrence in a set is declared by the database administrator when the schema is defined. 系隶属成员关系的一种说明,系中一个记录值的隶属不一定固定。系值中的隶属可以在不从数据 库中删除的情况下进行修改。当定义模式时,系中记录值的任选系隶属由数据库管理员来说明。 2. The specification of set membership such that a record occurrence can be disconnected from the set. Its membership in a set occurrence may be changed without its being deleted from the database. 系隶属的说明,记录值可以与系不连，系值中它的隶属可以在不从数据库删除的情况下改变。 参阅fixed member, mandatory member, retention class。 |
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