关联类及如何在语言级别实现多元关联

1.关联类

An association class is used to model an association as a class. Association classes often occur in many-to-one and many-to-many associations where the association itself has attributes.

As an example, consider a many-to-many association between classes Person and Company. The association could have properties; e.g., salary, jobClassification, startDate, etc. In this case, the association is more correctly modeled as an association class with attributes rather than trying to fold the attributes into one of the classes in the association.

理解问什么要使用关联类？

2.多元关联

不能像二元关联一样实现类之间的导航。二元关联可以通过reference实现，但是多元关联要通过方法才能实现。

例如要获取人员在项目中所用的语言，不能是Person.Language而是Language Person(Project p)。