You can assign Operations only to Call (synchronous and asynchronous) Messages. Only one Operation can be assigned to a Message. To assign an Operation to a Message Assign an Operation to a Message in the Message Specification window: If an Operation you are assigning to a Message has default parameter values, these default parameter values are assigned to the Message arguments. However, if the types of the Operation parameter and the Message argument do not match, the default parameter value is assigned to the Message argument. Names of operation parameters are displayed in message signature by default. However, you can change this behavior by opening the Symbol Properties dialog (right-click a Message and select Symbol Properties) and setting the Show Attribute/Parameter Names property to true to display them or false to hide them. To create a new Operation for a Message You can create a new Operation only if the Lifeline the Message is drawn to has a type assigned.
1. Draw a call Message between two Lifelines or select an existing Message on a diagram pane.
2. Open the Message Specification window.
3. Click the Signature (operation) property value cell and then select an Operation in the drop-down list.