是否需同时使用<<use>>与<<composition>>？UML类关联规范咨询

Hey there! Let's unpack your question about UML relationships between the School and TeacherRoom classes clearly:

1. First, clarify what each relationship means #

• <> (Composition): This is a strong form of aggregation where the TeacherRoom is a part of the School, with its lifecycle fully tied to the School. If the School instance is destroyed, the TeacherRoom instance it holds is also destroyed. Since your School only has one TeacherRoom instance, this is the correct core relationship to model.
• <> (Dependency): This represents a weaker relationship where one class uses the services of another, typically via method parameters, return values, or local variables. A dependency is shown as a dashed arrow pointing from the using class (School) to the used class (TeacherRoom).

2. Do you need both <> and <>? #

No, you don't. The composition relationship already implies that School uses TeacherRoom—after all, if School holds a reference to a TeacherRoom instance, it will almost certainly interact with that instance (call its methods, access its properties, etc.). Adding a separate <> dependency here is redundant because the usage is already obvious from the composition.

3. Can you remove the <> association? #

Absolutely. In standard UML practice, when a stronger relationship like composition (or even aggregation) exists between two classes, you don't need to add an explicit dependency arrow. The stronger relationship already covers the "usage" semantic.

4. UML Official Notation Recap #

• Composition: Draw a solid line from School to TeacherRoom, with a solid filled diamond attached to the School end (the "whole" side of the relationship). You can also add a multiplicity (like 1 next to TeacherRoom to indicate one instance) if needed.
• Dependency: Only use this dashed arrow if there's a usage that isn't covered by a stronger relationship (e.g., School creates a temporary TeacherRoom instance in a method without holding a reference to it long-term). But in your scenario, this isn't necessary.

内容的提问来源于stack exchange，提问作者Zubty