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Taking Complete Finite Prefixes To High Level, Symbolically

Nick Würdemann, Thomas Chatain, Stefan Haar, Lukas Panneke

TL;DR

This work identifies a more general class of nets with infinitely many reachable markings, for which an approach with an adapted cut-off criterion extends the complete prefix methodology, in the sense that the original algorithm cannot be applied to the P/T net represented by a high-level net.

Abstract

Unfoldings are a well known partial-order semantics of P/T Petri nets that can be applied to various model checking or verification problems. For high-level Petri nets, the so-called symbolic unfolding generalizes this notion. A complete finite prefix of a P/T Petri net's unfolding contains all information to verify, e.g., reachability of markings. We unite these two concepts and define complete finite prefixes of the symbolic unfolding of high-level Petri nets. For a class of safe high-level Petri nets, we generalize the well-known algorithm by Esparza et al. for constructing small such prefixes. We evaluate this extended algorithm through a prototype implementation on four novel benchmark families. Additionally, we identify a more general class of nets with infinitely many reachable markings, for which an approach with an adapted cut-off criterion extends the complete prefix methodology, in the sense that the original algorithm cannot be applied to the P/T net represented by a high-level net.

Taking Complete Finite Prefixes To High Level, Symbolically

TL;DR

This work identifies a more general class of nets with infinitely many reachable markings, for which an approach with an adapted cut-off criterion extends the complete prefix methodology, in the sense that the original algorithm cannot be applied to the P/T net represented by a high-level net.

Abstract

Unfoldings are a well known partial-order semantics of P/T Petri nets that can be applied to various model checking or verification problems. For high-level Petri nets, the so-called symbolic unfolding generalizes this notion. A complete finite prefix of a P/T Petri net's unfolding contains all information to verify, e.g., reachability of markings. We unite these two concepts and define complete finite prefixes of the symbolic unfolding of high-level Petri nets. For a class of safe high-level Petri nets, we generalize the well-known algorithm by Esparza et al. for constructing small such prefixes. We evaluate this extended algorithm through a prototype implementation on four novel benchmark families. Additionally, we identify a more general class of nets with infinitely many reachable markings, for which an approach with an adapted cut-off criterion extends the complete prefix methodology, in the sense that the original algorithm cannot be applied to the P/T net represented by a high-level net.
Paper Structure (37 sections, 16 theorems, 9 equations, 12 figures, 2 tables, 1 algorithm)

This paper contains 37 sections, 16 theorems, 9 equations, 12 figures, 2 tables, 1 algorithm.

Key Result

Proposition 1.7

Let $N$ be a high-level Petri net and $\varUpsilon$ its symbolic unfolding. Then $\mathcal{R}(N) = \{ \mathop{\mathrm{mark}}\nolimits(C,\theta)\,\mid\, C\in\mathcal{C}(\varUpsilon), \theta\in\Theta(C) \}$.

Figures (12)

  • Figure 1: A safe high-level Petri net $N$ in \ref{['fig:runEx']}, discussed in Example \ref{['ex:hlnet']}, and (a prefix of) the infinite symbolic unfolding $U(N)$ in \ref{['fig:runExUnf']}, discussed in Example \ref{['ex:prefix']}.
  • Figure 2: Illustration and example of nodes in color conflict.
  • Figure 3: The complete finite prefix of $\Upsilon(\mathop{\mathrm{Exp}}\nolimits(N))$ of the running example $N$ from Figure \ref{['fig:runEx']} calculated by the original ERV-Algorithm.
  • Figure 4: A symbolically compact net in \ref{['fig:ex-Nsc-vs-Nf']} where Alg. \ref{['alg:complpref']}, trying to build a complete finite prefix of the symbolic unfolding shown in \ref{['fig:ex-Nsc-vs-Nf-unf']}, does not terminate.
  • Figure 5: Fork And Join for $n=2$ in \ref{['fig:Independent-Diamond-2']} and $n=4$ in \ref{['fig:Independent-Diamond-4']}.
  • ...and 7 more figures

Theorems & Definitions (34)

  • Example 1.1
  • Definition 1.2: High-level occurrence net ChatainJ04
  • Example 1.3
  • Example 1.4: Color conflict
  • Definition 1.5: Configuration ChatainJ04
  • Definition 1.6: Instantiation of Configuration
  • Proposition 1.7
  • Proposition 1.8
  • Proposition 1.9
  • Definition 2.1: Complete prefix
  • ...and 24 more