Hierarchical FSM models

• Problem: how to reduce the size of the representation?

• Harel’s classical papers on StateCharts (language) and bounded concurrency (model): 3 orthogonal exponential reductions

• Hierarchy:

  • state a “encloses” an FSM
  • being in a means FSM in a is active
  • states of a are called OR states
  • used to model pre-emption and exceptions

• Concurrency:

  • two or more FSMs are simultaneously active
  • states are called AND states

• Non-determinism:

  • used to abstract behavior

error

normal

recovery

odd

even

done

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