statechart for the washing machine - ut · statechart for the washing machine 1 state modeling ......

Statechart for the washing machine

State modeling -- Luciano García-Bañuelos 1

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State explosion and history


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What if the “power” button can be clicked at anytime?

What if we want to come back to the same state we left?

State explosion


  If we consider that each attribute in a class defines at least two possible states (e.g. boolean values)

  If we have “n” classes with “m” attributes each (let’s assume that all classes have the same number of attributes)   Possible states: 2nm

  What if the state space of each variable > 2 ?

Composite states


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The transition can be fired from any internal state

Contour transitions


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The event “stop” will move to state “first” independently of the current

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History


  Return to a previously visited hierarchical state   Shallow history: just the current level

  Deep history: includes all nested states

  Some times it is useful to clear history   clear-history(state) clh(state)   clear-history(state*) clh(state*)

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History


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Deep vs Shallow history


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Completing transitions


  Triggered by a completion event   generated automatically when an immediately nested state

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Triggering rules


  Two or more transitions may have the same event trigger   inner transition takes precedence   if no transition is triggered, event is discarded

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Order of activities in nested models


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Execution sequence:

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Orthogonal states


  Multiple simultaneous perspectives on the same entity

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Orthogonal regions


  Combine multiple simultaneous descriptions

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Parallelism in Statecharts


  All mutually orthogonal regions detect the same events and respond to them “simultaneously”   usually reduces to interleaving of some kind

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Synchronization


  Concurrent orthogonal regions/states can be synchronized by transition guards

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This transition can only be fired when A.C is in M state

Splitting of control: Forks


  Forks allow to split the control into concurrent paths   It ensures the concurrent activation of state activities

  Note that the control paths are synchronized implicitly, i.e. completion transitions

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Merging of control and exceptions


  UML provides a notation for specifying the merging of control in a explicit way

  Note that the escaping branch is similar to raising an exception

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Class aggregation and their state diagrams


  A state diagram is a collection of state diagrams   Class aggregation will

usually require to combine the state diagrams of all parts

  The whole can be thought as a set of orthogonal regions

statechart for the washing machine - ut · statechart for the washing machine 1 state modeling ......

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