Creating an aggregation
An aggregation is an Association that has its Aggregation property set to 'part of' or 'made up of'.
For information about creating a composite aggregation between Activities, which creates a Call Behavior Action, click here
To create an aggregation on a class diagram:
1. On the Class Diagram tab, click the 
Composite Aggregation or 
Shared Aggregation button.
Composite Aggregation or Shared Aggregation button.2. On the diagram, click the source item.
The source item can be a Class, Data Type, Interface or Signal.
3. On the diagram, click the destination item.
The destination item can be a Basic Type, Class, Data Type, Interface, Signal or Type Definition.
4. Type the name of the aggregation, and then press the Enter key.