Events and Messages

Events and Messages

Participants change state on a timing diagram in response to events. These events might be the invocation of a message or they might be something else, such as a message returning after it has been invoked. The distinction between messages and events is not as important on a timing diagram as it is on sequence diagrams. The important thing to remember is that whatever the event is, it is shown on a timing diagram to trigger a change in the state of a participant.

An event on a timing diagram is shown as an arrow from one participant's state-linethe event sourceto another participant's state-linethe event receiver (as shown in Figure).

Events on a timing diagram can even have their own durations, as shown by event1 taking 1 unit of time from invocation by p1:Participant1 and reception by p2:Participant2

Adding events to the timing diagram is actually quite a simple task, because you have the sequence diagram from Figure to refer to. The sequence diagram already shows the messages that are passed between participants, so you can simply add those messages to the timing diagram, as shown in Figure.

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