Composition relationships

A composition relationship, which was named composition association relationship in UML 1.4, represents whole–part relationships and is a form of aggregation. A composition relationship specifies that the lifetime of the part classifier is dependent on the lifetime of the whole classifier.

In a composition relationship, data usually flows in only one direction (that is, from the whole classifier to the part classifier). For example, a composition relationship connects a Student class with a Schedule class, which means that if you remove the student, the schedule is also removed.

You can name any association to describe the nature of the relationship between the two classifiers; however, names are unnecessary if you use association end names.

A composition relationship appears as a solid line with a filled diamond at the association end, which is connected to the whole, or composite, classifier.

The image shows two classes, Student and Schedule, joined by a composition relationship.

Parent topic: Relationships between model elements

Related tasks
Adding relationships to diagrams

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