Aggregation specifies a relationship in which one class represents the components of a second class, and the second class constitutes the whole. The class Consortium is the aggregation of its member banks.

Aggregation is specified in the definition dialog of an association. It is represented by a diamond-shaped notation on the association line affixed to the class that makes up the whole.

Composite aggregation is a stronger form of aggregation. It is represented by a filled-in diamond is attached to the association end at the class that is the composite aggregate.