UML Tutorials - Herong's Tutorial Examples - v1.03, by Dr. Herong Yang
Activity Diagram - Accept Event Notation
This section describes the Accept Event Notation used in a UML Activity Diagram. An Accept Event Notation represents an action that waits for an event to arrive from outside and processes it.
An Accept Event Notation is a graphical notation used in a UML Activity Diagram to represent an accept event action that waits for a certain event to arrive from outside of the activity.
There are two types of accept event actions in an UML activity diagram with different notations:
1. Recurring Accept Event Action - Waits for multiple events to arrive and processing events and passing the execution control to the next action. Once a recurring accept event is started, it never stops. A Recurring Accept Event Action Notation is drawn as a concave pentagon with on incoming flow control, which starts immediately when the parent activity starts and remains to accept events all the time.
2. One-Time Accept Event Action - Waits for one event to arrive and stops after processing that event and passing the execution control the next action. A One-Time Accept Event Action Notation is drawn as a concave pentagon with one incoming flow control, which connects to the previous action that triggers the start of this Accept Event action.
The following picture gives a good example of using Accept Event Notations in an Activity Diagram.
The first action in the diagram is a Recurring Accept Event Action called "Listen Order Request", which continuously waits and accepts new order requests. Each time a new order request is accepted, it will invoke the "Process Order" action, which in turn invokes the "Request Payment" action.
The "Request Payment" sends a payment request signal to the outside and invokes the "Wait for Payment" action, which is a One-Time Accept Event Action. It waits for the payment event to arrive, invokes the "Ship Order" action, then ends itself until it is invoked again by the "Request Payment" action.
Note that in some UML drawing tools, An Accept Event Notation may be called as Accept Signal, Receive Event, Receive Signal.
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