Transitions (OOM)

A transition is an oriented link between states, which indicates that an element in one state can enter another state when an event occurs (and, optionally, if a guard condition is satisfied). The expression commonly used in this case is that a transition is fired.

A transition can be created in the following diagrams:

Statechart Diagram

The statechart diagram transition is quite similar to the flow in the activity diagram, with the addition of a few properties:

A trigger event: it is the event that triggers the transition (when you copy a transition, the trigger event is also copied)
A trigger action: it specifies the action to execute when the transition is triggered

The activity diagram is a simplification of the statechart diagram in which the states have only one action and the transition has a triggered event corresponding to the end of the action.

The transition link is represented as a simple arrow. The associated event, the condition and the action to execute are displayed above the symbol.

The following rules apply:

Reflexive transitions only exist on states
A trigger event can only be defined if the source is a start or a state
Two transitions can not be defined between the same source and destination objects (parallel transitions). The Merge Model feature forbids this.

Note: When transitions are compared and merged by the Merge Model feature, they are matched by trigger event first, and then by their calculated name. When two transitions match, the trigger actions automatically match because there cannot be more than one trigger action.