UML Class Relationships

Question

I would like to confirm whether I am on the right track when identifying common UML class relationships. For example, is the relationship between:

1

Answer 1

The UML spec is incoherent regarding the aggregation vs. composition definitions. They are not properly defined, as has been shown by several authors (Henderson-Sellers among others). I suggest you don't waste your time trying to determine whether something in your mind maps best to one or the other. There is no right answer. :-)

Myself, I often use an abstract whole/part relationship to model wholes and parts. Semantics about binding, lifetime and exclusivity can be given by pseudocode or annotations. There are so many different cases and scenarios that trying to foresee all the possibilities beforehand is not worth it. Edit: this approach was proposed by Henderson-Sellers and myself to OMG during the review round of an earlier version of UML, a few years ago. Unfortunately, it didn't make it. :-)

Even if UML were coherent, there are not right or wrong models; some models are useful and some are not. You create models depending on the purpose you pursue.