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1

Generation of synchronizing state machines from a transition system: A region-based approach

Teren Viktor, Cortadella Jordi, Villa Tiziano

International Journal of Applied Mathematics and Computer Science

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2023

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Vol. 33, no. 1

133--149

EN

Transition systems (TSs) and Petri nets (PNs) are important models of computation ubiquitous in formal methods for modeling systems. A crucial problem is how to extract, from a given TS, a PN whose reachability graph is equivalent (with a suitable notion of equivalence) to the original TS. This paper addresses the decomposition of transition systems into synchronizing state machines (SMs), which are a class of Petri nets where each transition has one incoming and one outgoing arc. Furthermore, all reachable markings (non-negative vectors representing the number of tokens for each place) of an SM have only one marked place with only one token. This is a significant case of the general problem of extracting a PN from a TS. The decomposition is based on the theory of regions, and it is shown that a property of regions called excitation-closure is a sufficient condition to guarantee the equivalence between the original TS and a decomposition into SMs. An efficient algorithm is provided which solves the problem by reducing its critical steps to the maximal independent set problem (to compute a minimal set of irredundant SMs) or to satisfiability (to merge the SMs). We report experimental results that show a good trade-off between quality of results vs. computation time.

2

Regular Orthomodular Posets

Borzyszkowski Andrzej M.

Fundamenta Informaticae

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2019

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Vol. 166, nr 1

15--28

EN

Rozenberg and Ehrenfeucht has shown a duality between 2-structures (a.k.a. transition systems) and (elementary) Petri nets. The tool has been the notion of a region of a 2-structure, the regions then define a Petri net. Bernardinello et al. has observed that the regions of a 2-structure form an orthomodular poset and there is a similar relation between 2-structures and orthomodular posets. While in the theory of 2-structures we may ask if a 2-structure is full and forward closed, the analogous notion for orthomodular posets is their regularity. In the present paper we study the problem of closing a given orthomodular poset to a regular one. This is a dual problem to closing a 2-structure, which has been studied by the author earlier. Also, as in a seminal work of Rozenberg and Ehrenfeucht, one can be interested in a concrete representation, i.e. as a family of sets. We show here an appropriate construction for orthomodular posets too.

3

Analysis and Synthesis of Weighted Marked Graph Petri Nets : Exact and Approximate Methods

Devillers Raymond, Hujsa Thomas

Fundamenta Informaticae

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2019

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Vol. 169, nr 1-2

1--30

EN

Numerous real-world systems can be modeled with Petri nets, which allow a combination of concurrency with synchronizations and conflicts. To alleviate the difficulty of checking their behaviour, a common approach consists in studying specific subclasses. In the converse problem of Petri net synthesis, a Petri net of some subclass has to be constructed efficiently from a given specification, typically from a labelled transition system (lts) describing the behaviour of the desired net. In this paper, we focus on a notorious subclass of persistent Petri nets, the weighted marked graphs (WMGs), also called generalised (or weighted) event (or marked) graphs or weighted T-nets. In such nets, edges have multiplicities (weights) and each place has at most one ingoing and one outgoing transition. Although extensively studied in previous works and benefiting from strong results, both their analysis and synthesis can be further investigated. We provide new behavioural properties of WMGs expressed on their reachability graph, notably backward persistence and strong similarities between any two sequences sharing the same starting state and the same destination state. Besides, we design a general synthesis procedure aiming at the WMG class. Finally, when no solution to the synthesis problem exists, i.e., when the given lts is not WMG-solvable, we show how to construct a WMG whose reachability graph is a minimal over-approximation of the given lts.

4

Minimal Regions of ENL-Transition Systems

Koutny M., Pietkiewicz-Koutny M.

Fundamenta Informaticae

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2010

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Vol. 101, nr 1/2

45-58

EN

One of the possible ways of constructing concurrent systems is their automated synthesis from behavioural specifications. In this paper, we look at a particular instance of this approach which aims at constructing GALS (globally asynchronous locally synchronous) systems from specifications given in terms of transition systems with arcs labelled by steps of executed actions. GALS systems are represented by Elementary Net Systems with Localities (ENL-systems), each locality defining a set of co-located actions. The synthesis procedure is based on the regions of transition systems and we provide a number of criteria aimed at generating a minimal set of regions (conditions) of an ENL-system generating a given transition system.

5

Process Discovery using Integer Linear Programming

van der Werf J.M.E.M., van Dongen B.F., Hurkens C.A.J., Serebrenik A.

Fundamenta Informaticae

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2009

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Vol. 94, nr 3/4

387-412

EN

The research domain of process discovery aims at constructing a process model (e.g. a Petri net) which is an abstract representation of an execution log. Such a model should (1) be able to reproduce the log under consideration and (2) be independent of the number of cases in the log. In this paper, we present a process discovery algorithm where we use concepts taken from the language-based theory of regions, a well-known Petri net research area. We identify a number of shortcomings of this theory from the process discovery perspective, and we provide solutions based on integer linear programming.

6

Synthesis of Elementary Net Systems with Context Arcs and Localities

Koutny M., Pietkiewicz-Koutny M.

Fundamenta Informaticae

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2008

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Vol. 88, nr 3

307-328

EN

We investigate the synthesis problem for ENCL-systems, defined as Elementary Net Systems extended with context (inhibitor and activator) arcs and explicit event localities. Since colocated events are meant to be executed synchronously, the behaviour of such systems is captured by step transition systems, where arcs are labelled by sets of events rather than by single events. We completely characterise transition systems generated by ENCL-systems after extending the standard notion of a region - defined as a certain set of states - with explicit information about events which, in particular, are responsible for crossing its border. As a result, we are able to construct, for each such transition system, a suitable ENCL-system generating it.

7

Synthesising Elementary Net Systems with Inhibitor Ares from Step Transition Systems

Pietkiewicz-Koutny M.

Fundamenta Informaticae

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2002

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Vol. 50, nr 2

175-203

EN

We here consider transition systems of Elementary Net Systems with Inhibitor Arcs. There are basically two different types of non-interleaving semantics of such Petri nets, the a-posteriori and a-priori semantics. The synthesis problem for Elementary Net Systems with Inhibitor Arcs executed under the a-priori semantics (ENI) was solved in [18]. In this paper we completely characterise transition systems which can be generated by Elementary Net Systems with Inhibitor Arcs executed under the a-posteriori semantics (ENIapost). This is achieved by adapting the notion of a step transition system, i.e. one in which arcs are labelled by sets of events executed concurrently. In developing the model, we follow the standard approach in which the relationship between nets and their transition systems is established via the notion of a region. We define, and show consistency of, two behaviour preserving translations between nets and transition systems. We then compare transition systems which are generated by ENIapost and ENI-systems (called respectively TSENIapost and TSENI transition systems).

8

The synthesis problem for Elementary Net Systems with Inhibitor Arcs

Pietkiewicz-Koutny M.

Fundamenta Informaticae

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1999

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Vol. 40, Nr 2,3

251-283

EN

We investigate the synthesis problem for the Elementary Net Systems with Inhibitor Arcs (ENI-systems) executed according to the a-priori semantics. We characterise transition systems generated by ENI-systems, called TSENI transition systems, by adapting the notion of a step transition system whose arcs are labelled by sets of concurrently executed events. The relationship between the ENI-systems and TSENI transition systems is established via the notion of a region. We define, and show consistency of, two behaviour preserving translations between nets and transition systems. We also discuss how to optimise the synthesis procedure by using only minimal regions and selected inhibitor arcs.