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umlstate-diagram

State transition with only a guard in UML state diagrams

As far as I understand, you can do a transition in UML state diagrams for example with:

  • Event[Guard]/Action
  • Event[]/Action
  • Event

http://www.sparxsystems.com/resources/uml2_tutorial/uml2_statediagram.html

Is it also possible/valid in UML to have a transition only with a Guard and no Event & Action?

  • No Event[Guard]/No Action

Thanks!

Solution

  • In UML this is allowed, such as in EA. So each transition in a state chart can have a set of events, which can be empty, can have a guard or not, and can have an action or not.

    You need to be carefull with the tools, as most of the tools have some deviations and limitations or stick to an old UML version. So not any tool allows everything that is defined by UML and some tools (esp. EA) is far more permissive. It sometimes depends on what you want to do with the model and diagrams. If a dynamic diagram is inteneded for simulation,the rules are mostly far more strict and not any UML construct is allowed. A tool that is far more conform to the UML standard in most of its revisions is MagicDraw.