英文:
How to avoid circular association (Class Diagram)
问题
我有一个Project类，其中包含一个Objective。一个Objective可以有多个Projects。一个Meeting可以与一个Project（其中包含一个Objective）或Objective相关联。如何在类图中表示这种关系？
我知道不应该这样做。
英文:
I have a Project class that has one Objective. an Objective that has many Projects. a Meeting that can be associated to a Project (which has an Objective) or Objective. How can I represent this relationship in a Class Diagram
I know it shouldn't be done this way
答案1
得分: 3
在UML中，存在循环关联绝对没有问题。这在你建模现实生活领域时非常常见。你甚至可以有自关联类在一个循环关联中，这仍然不会成为问题。
你唯一的建模挑战是准确表示：
> 一个Meeting可以与一个Project（它有一个Objective）或Objective相关联。
因此，你首先需要澄清：
- 它可以是两者之一吗（你的图表已经包含了这一点）？
- 它可以是两者都吗？如果可以：
- 会议的目标是否可以与项目目标不同（你的图表仍然包含了这一点）？
- 还是会议和项目的目标必须保持一致（请参阅我的其他答案，如何使用OCL表示直接和间接关联类之间的约束）？
- 它必须是其中一个，而不能同时是两者吗（请参阅这个问题以获取有关此主题的最佳最近答案）？
英文:
There is absolutely no problem in UML with circular associations. This is common business as soon as you model real life domains. You could even have self-associating classes in a circular association, and it still wouldn't be an issue.
Your only modelling challenge is to represent accurately:
> A Meeting that can be associated to a Project (which has an Objective) or Objective.
You must therefore first disambiguate:
-
can it be none of the two (your diagram gets it) ?
-
can it be both? If yes:
- can the meeting's objective be different from the project objective (your diagram still gets it) ?
- or shall objectives of the meeting and the project be aligned (see my other answer here, how to express constraints between direct and indirect associated classes using OCL)
-
must it be the one or the other but not both (see this question for the best recent answers on this topic)?
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