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umlstatediagramfsm

UML state diagrams and Moore/Mealy machines

How to model Moore and Mealy machines with UML state diagrams? Besides, how to represent outputs in those diagrams? Through Actions?

Solution

  • UML state diagrams have the characteristics of both Mealy and Moore state machines.

    To represent a pure Mealy machine, you use only actions on transitions:

    stateA -- TRIGGER [guard] / action() --> stateB

    To represent a pure Moore machine, you use only entry or exit actions to states, but you don't use actions on transitions:

    stateA
   entry/ actionA();

stateB
   entry/ actionB();

    When you use both actions on transitions and entry/exit actions in states, you have a mix of Mealy and Moore machines.