...elationship)、依赖关系(Dependent relationship)、支配关系(Dominant relationship)、强制关系(Mandatory relationship)的定义与区别? 3.从概念数据模型转换为物理数据模型时,实体之间的关系转换规则是什么?
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非强制关系在数据库关系图中由虚线表示。
An unenforced relationship is represented in a database diagram by a dashed line.
如果为实线,则当在外键表中添加或修改行时,DBMS将强制关系的引用完整性。
If the line appears solid, the DBMS enforces referential integrity for the relationship when rows are added or modified in the foreign-key table.
如果为点线,则当在外键表中添加或修改行时,DBMS不强制关系的引用完整性。
If the line appears dotted, the DBMS does not enforce referential integrity for the relationship when rows are added or modified in the foreign-key table.
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