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umlclass-diagram

How to improve/edit in this UML class diagram?

How can I improve this UML class diagram and what mistakes I made?

I'm really confused about the relationship between Expense and Category, because Category and Expense can exist by themselves: you can register Expense and not assign it to a category, or do the opposite, you can add new Categories to the categories list, and so on...

Do I really need separate List classes?

enter image description here

Solution

  • I would just make your CategoryList the Category class and delete the latter. I don't know your domain, but assuming an expense can be assigned one or more categories you can clarify this by adding a multiplicity. You should also drop the shared composition (hollow diamond) as it does not add any real information to your model.

    Edit According to your comment I would model it like this:

    enter image description here

    The representation of Category as a list would be task of some View or Controller that represents existing categories. One could think of your CategoryList class as such a controller.