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UML state diagrams: make sequences of object states visible

Events (Actions) can describe in more detail under which conditions a state is exitedto switch to the next state. During the transition from the initial state to the first real state, it is not necessary; further event details are optional. If no event is specified, it means that it will occur automatically as soon as all activities in previous states have been completed.

A NO event (trigger / ANY trigger) indicates that the event basically always present is. Events can be named as behavior specification within the state or within the state transition (see transition).

A triggering event must have the following three conditions fulfill:

  • entry: The event is triggered automatically when entering a state, i. H. in all incoming transitions.
  • exit: The event is triggered when a state is exited, i. H. in all outgoing transitions.
  • do: The event is triggered again and again if the state is not changed.

These behavior specifications can be noted within the state in order to show in a simplified manner the behavior under which the state changes. There are two possibilities for the graphical representation of such triggers: On the one hand, they can be identified within the corresponding state, as the following state diagram example illustrates: