er图中的基数

时间:2018-01-15 20:53:31

标签: cardinality

(0,n)和(1,n)基数之间的区别是什么以及如何在给定情况下区分它们。 例如,给定完整性约束,您必须设计er图。我知道首先我应该为每个实体和关系定义基数。

1 个答案:

答案 0 :(得分:0)

it depends on your mini-world. for example, in a company, there should be no department without at least one employee. in another company, it is allowed to have a department without any employees related to that deparment.