DECIDABILITY QUESTIONS FOR PETRI NETS

  • Authors:
  • M. Hack

  • Affiliations:
  • -

  • Venue:
  • DECIDABILITY QUESTIONS FOR PETRI NETS
  • Year:
  • 1976

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Abstract

An understanding of the mathematical properties of Petri Nets is essential when one wishes to use Petri Nets as an abstract model for concurrent systems. The decidability of various problems which arise in this context is an important aspect of this question. The fact that these problems also arise in the context of other mathematical theories, such as commutative semigroups, closure under linear relations, Matrix Context-Free grammars, or Weak Counter Automata, provides further motivation. The Reachability Problem for Vector Addition Systems - whose decidability is still an open question - is of central importance. We show that a number of Petri Net problems are recursively equivalent to this problem. These include the Liveness Problem (e.g. can a system reach a deadlocked state?), the persistence problem (can a given transition ever be disabled by the firing of another transition?), and the membership and emptiness problems for certain classes of languages generated by Petri Nets. The power of the unrestricted Petri Net model is illustrated by various undecidable equivalence results. In particular, we show that the equality of Reachability Sets and the equivalence of two Petri Nets in terms of their language-generating capability are recursive undecidable. It is hoped that the constructions used to prove our results will shed some light on the source of the complexities of the unrestricted Petri Net model, and may eventually permit us to achieve an optimal balance between representational transparency and analytical power of the Petri Net model.