Assessing SMT and CLP approaches for workflow nets verification

Abstract

In the actual business world, companies rely more and more on workflows to model the core of their business processes. In this context, the focus of workflow analysts is made on the verification of workflows specifications, in particular of modal specifications that allow the description of necessary or admissible behaviors. The design and the analysis of business processes commonly relies on workflow nets, a suited class of Petri nets. The goal of this paper is to evaluate and compare in a deep way two resolution methods—satisfiability modulo theory and constraint logic programming—applied to the verification of modal specifications over workflow nets. Firstly, it provides a concise description of the verification methods based on constraint solving. Secondly, it introduces the toolchain developed to automate the full verification process. Thirdly, it describes the experimental protocol designed to evaluate and compare the scalability and efficiency of both resolution approaches and reports on the obtained results. Finally, these obtained results are discussed in detail, lessons learned from these experiments are given, and, on the basis of experiments feedback, directions for improvement and future work are suggested.

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Notes

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    www.smtcomp.org.

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    www.minizinc.org/challenge.html.

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Correspondence to Fabien Peureux.

A Appendix: Verifying modal specification using model checking

A Appendix: Verifying modal specification using model checking

In this appendix we describe the methodology used to verify modal specifications using a CTL Petri net model checker such as LoLa [30].

As stated in Sect. 2 modal specifications are a proper subset of CTL, it is therefore possible to check any modal specifications of a given workflow net using any CTL Petri net model checker. To this end, the considered workflow net needs to be transformed into an equivalent Petri net such that the validity of any modal specifications is equivalent to the validity of the corresponding CTL formulae. The aim of this transformation is to introduce for each transition t a new place \(p_t\) which is marked if and only if t has been fired at least once during an execution marking the final place o.

To produce a Petri net \(\tilde{N}\) from a workflow net \(N = \langle P,T,F \rangle \) the transformation proceeds as follows. For each transition \(t \in T\) the transformation introduces two new places, respectively, denoted \(f_t\) and \(p_t\). Further, the transformation then replaces each transition t by two transitions, respectively, denoted \(t_f\) and \(t_e\) such that:

  • \(^{\bullet }t_f = ^{\bullet }t \cup \{f_t\}\)

  • \(t_f^{\bullet } = t^{\bullet } \cup \{p_t\}\)

  • \(^{\bullet }t_e = ^{\bullet }t \cup \{p_t\}\)

  • \(t_e^{\bullet } = t^{\bullet } \cup \{p_t\}\)

Note that if the state space of N is finite, then the state space of \(\tilde{N}\) is finite too.

The initial marking of \(\tilde{N}\) is the marking assigning a single token to place i and places \(f_t\) where \(t \in T\) (and none to other places).

By construction, for any execution \(\sigma \) of N, there exist a corresponding execution \(\tilde{\sigma }\) of \(\tilde{N}\) obtained by replacing, for every transition \(t \in T\), the first occurrence of t by \(t_f\) and the following occurrences of t by \(t_e\). Conversely, for any execution \(\tilde{\sigma }\) of \(\tilde{N}\) there exists a corresponding execution \(\sigma \) of N obtained by replacing, for every transition \(t \in T\), all occurrences of \(t_f\) and \(t_e\) by t.

Further, given a modal formula \(f \in S\) of the workflow net N, we define CTL(f) as the formula obtained after replacing, for every transition \(t \in T\), the corresponding terminal symbols of the modal formula f by \(p_t=1\).

Consequently, as for each transition t the new place \(p_t\) is marked if and only if t has been fired at least once during an execution, we have:

  • \(N \models _{may} f \Leftrightarrow \tilde{N} \models EF (o=1) \Rightarrow (CTL(f))\)

  • \(N \models _{must} f \Leftrightarrow \tilde{N} \models AF (o=1) \Rightarrow (CTL(f))\)

This enables the verification of modal specifications described in this paper using CTL model checker, and consequently this link makes it possible to compare verification approaches by constraint solving and by model checking.

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Bride, H., Kouchnarenko, O., Peureux, F. et al. Assessing SMT and CLP approaches for workflow nets verification. Int J Softw Tools Technol Transfer 20, 467–491 (2018). https://doi.org/10.1007/s10009-018-0486-5

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Keywords

  • Workflow nets
  • Modal specifications
  • Verification method
  • Experimental comparison
  • Satisfiability modulo theory
  • Constraint solving problem