umldiagramtransitionstate-diagram

One transition with multiple events in UML State diagram

We are learning in school that behavioral State diagram's transition has syntax:

list of events [guard condition] / list of actions

But I couldn't find any example on Internet where is used transition with multiple events. Is it really possible? If yes, how does it behave? Does it mean that transaction is realized when one of this events occurs (and of course condition is fulfilled)?

Solution

  • Yes, a transition can be triggered by one of many events in a list. You would use such a construct to avoid multiple lines between states, making a tidier diagram.

    Here is what the 2.5 spec says:

    14.2.3.9.2 Enabled Transitions

    A Transition is enabled if and only if:

    • [ . . . ]

    • At least one of the triggers of the Transition has an Event that is matched by the Event type of the dispatched Event occurrence.

    These logically OR'ed transitions are specified textually as a comma-separated list on the transition, as specified in §14.2.4.9:

    [<trigger> [‘,’ <trigger>]* [‘[‘ <guard>’]’] [‘/’ <behavior-expression>]]