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A transition is a directed relationship between a source vertex and a target vertex.

It may be part of a compound transition, which takes the State Machine from one state configuration to another, representing the complete response of the state machine to an occurrence of an event of a particular type.

There are two kinds of Transitions:

External Transitions (default)

An internal transition executes without exiting or re-entering the state in which it is defined. This is true even if the state
machine is in a nested state within this state.

Internal Transitions

An internal transition executes without exiting or re-entering the state in which it is defined. This is true even if the state machine is in a nested state within this state.
An advantage of the Internal Transtions is that it can be used like a DoAction/Activity with a Guard or Trigger. 

Execution Sequence

Every transition, except for internal causes exiting of a source state, and entering of the target state.
These two states, which may be composite, are designated as the main source and the main target of a transition.

The order of execution of entry/exit activities as well as transition effects is as defined in UML 2.4

Note that for composite states, the active states are exited recursively starting with the innermost state. Then the transition effect is executed, after which the target states are entered recursively, starting with the outermost state. Entry and exit points allow even finer control over the execution order of effects. For entry-points, this is the order of execution:

  1. The active states are exited like with normal transitions.
  2. The transition effect of the incoming transition is executed.
  3. The entry action of the composite state is performed.
  4. The transition effect of the outgoing transition will be executed. 
  5. The target states are entered like with normal transitions.

For exit-points the behavior is analogue:

  1. The active states are exited like with normal transitions.
  2. The transition effect of the incoming transition is executed.
  3. The exit action of the composite state is performed.
  4. The transition effect of the outgoing transition is executed.
  5. The target states are entered like with normal transitions.


See also

Transition priorities

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