Aggregation Association Relationships

An aggregation association is a relationship that indicates that one classifier is a part of or subordinate to another classifier. Data flows from the whole classifier to the part. A part classifier may belong to more than one aggregate classifier, and it may exist independently of the aggregate. Aggregation is closely related to composition. For details, see Composition Associations Relationships.

Note Aggregation associations do not have to be unidirectional. Also, whether the "part" may belong to more than one aggregate, or whether it may exist independently, is indicated by the multiplicity on the aggregate end.

For example, a "Department" class can have an aggregation relationship with a "Company" class, indicating that the department is part of the company (the aggregate).

An aggregation association appears as a solid line with an unfilled diamond at the association end connected to the classifier representing the whole.

You can name any association to describe the nature of the relationship between the two classifiers; however, names are typically not needed, especially if you use association end names.

• Adding and Modifying Relationships
• Association Relationships
• Specifying Kinds of Association Relationships

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