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Moore or Mealy model

Moore and Mealy models are the basic two models of state machines as defined in the literature. To understand the differences between them the actions (outputs) must be defined and bound to state changes. The technical note “Moore or Mealy model?” discusses both models and shows that the optimal solution is achieved when features of both models are used in a mixed model. Although the concepts of these two models are useful when performing certain theoretical studies, they are also interesting for software developers, and StateWORKS makes the use of a mixed model easy and effective.


Mealy and Moore models are the basic models of state machines. A state machine which uses only Entry Actions, so that its output depends on the state, is called a Moore model. A state machine which uses only Input Actions, so that the output depends on the state and also on inputs, is called a Mealy model. The models selected will influence a design but there are no general indications as to which model is better. Choice of a model depends on the application, execution means (for instance, hardware systems are usually best realized as Moore models) and personal preferences of a designer or programmer. In practice, mixed models are often used with several action types.

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