A Message/Stimulus line can be notated by its type of synchronization. There are a number of types of synchronization that can be modeled.
To select the type of synchronization for a line
1 Select Edit (from drop-down list accessed through right-click, or Edit menu) to open the message's definition.
2 Click the Symbol tab, and then select the synchronization type from the drop down list.
Synchronization types
Simple
Synchronous
An operation begins only when the sending object has initiated the action and the receiving object is ready to accept it; both objects might wait indefinitely until they are both ready to proceed.
Asynchronous
The sending object can send a message regardless of the ability of the receiving object to accept it. It is drawn with a half arrowhead (only one wing instead of two).
Time-out
The same as synchronous, except that the sending object will wait a specified amount of time for the receiving object to receive it.
Balking
The same as synchronous, except that the sending object will abandon the action immediately if the receiving object is not ready.
Procedure call, Procedure call return
A procedure call is drawn as a full arrowhead. The return is shown as a dashed arrow. In procedural flow of control, the return arrow can be omitted (it is considered implicit). For non-procedural flow of control, including parallel processing and asynchronous messages, returns should be shown explicitly.
Wait
When modeling a concurrent system a full arrowhead shows the yielding of a thread of control (wait semantics).
No-wait
When modeling a concurrent system a half arrowhead shows the sending of a message without yielding control (no-wait semantics).
