Interactions and Activities
The behavioral aspects of Interactions and Activities are modeled using the Behavior tab of the element's Properties dialog, on which you assign parameters and return types to the elements.
Access On diagram or in Project Browser | Right-click on element | Properties > Behavior
Click on the Edit Parameters button to edit the element's parameters. When you create a new parameter using the dialog, it internally creates an Activity Parameter Node for an Activity or an Interaction Parameter for an Interaction.
In the Return field, click on the drop-down arrow and select the return type of the element. Alternatively, click on the Select Behavior ( ... ) button and use the Select Type screen to locate the appropriate classifier.
The Specification field is populated automatically when an operation is associated with the Activity as a behavior.