Creating a composite aggregation between two activities on a block definition diagram (SysML)
When a Block Definition Diagram shows a composite aggregation between two Activities, that composite aggregation represents a call that is made through a Call Behavior Action. As such, when you create a composite aggregation between two Activities, Modeler creates a Call Behavior Action under the calling Activity. When you select the composite aggregation on the Block Definition Diagram, the Property Pages show the properties of the Call Behavior Action.
To create a composite aggregation between two activities on a block definition diagram:
1. On the diagram's tab, click the 
Composite Association button.
Composite Association button.2. Click the calling Activity, and then click the called Activity.
3. Rename the Call Behavior Action that is created under the calling Activity.