Rémi Morin

Recognizable Sets of Message Sequence Charts

High-level Message Sequence Charts are a well-established formalism to specify scenarios of communications in telecommunication protocols. In order to deal with possibly unbounded specifications, we focus on star-connected HMSCs. We relate this subclass with recognizability and MSO-definability by means of a new connection with Mazurkiewicz traces. Our main result is that we can check effectively whether a star-connected HMSC is realizable by a finite system of communicating automata with possibly unbounded channels.

Pomsets for local trace languages

Mazurkiewicz traces can be seen as equivalence classes of words or as pomsets. Their generalisation by local traces was formalized by Hoogers, Kleijn and Thiagarajan as equivalence classes of step firing sequences. First we introduce a pomset representation for local traces. Extending Buchis Theorem and a previous generalisation to Mazurkiewicz traces, we show then that a local trace language is recognized by a finite step transition system if and only if its class of pomsets is bounded and definable in the Monadic Second Order logic. Finally, using Zielonkas Theorem, we show that each recognizable local trace language is described by a finite safe labelled Petri net. The complete version [22] of this paper is accessible on the web.

Unfolding synthesis of asynchronous automata

Zielonkas theorem shows that each regular set of Mazurkiewicz traces can be implemented as a system of synchronized processes provided with some distributed control structure called an asynchronous automaton. This paper gives a new algorithm for the synthesis of a non-deterministic asynchronous automaton from a regular Mazurkiewicz trace language. Our approach is based on an unfolding procedure that improves the complexity of Zielonkas and Pighizzinis techniques: Our construction is polynomial in terms of the number of states but still double-exponential in the size of the alphabet. As opposed to Metiviers work, our algorithm does not restrict to acyclic dependence alphabets.

Synthesis of safe message-passing systems

We show that any regular set of basic MSCs can be implemented by a deadlock-free communicating finite-state machine with local termination: Processes stop in local dead-states independently from the contents of channels and the local states of other processes. We present a self-contained, direct, and relatively simple construction based on a new notion called context MSC.

The Pros and Cons of Netcharts

Netcharts have been introduced recently by Mukund et al. in [17]. This new appealing approach to the specification of collections of message sequence charts (MSCs) benefits from a graphical description, a formal semantics based on Petri nets, and an appropriate expressive power. As opposed to high-level MSCs, any regular MSC language is the language of some netchart. Motivated by two open problems raised in [17], we establish in this paper that the questions

Black Box Unfolding with Local First Search

McMillans unfolding approach to the reachability problem in 1-safe Petri nets and its later improvements by Esparza-Romer-Vogler have proven in practice as a very effective method to avoid stateexplosion. This method computes a complete finite prefix of the infinite branching process of a net. On the other hand,the Local First Search approach (LFS) was recently introduced as a new partial order reduction technique which characterizes a restricted subset of configurations that need to be explored to check local properties. In this paper we amalgamate the two approaches: We combine the reduction criterion of LFS with the notions of an adequate order and cutoff events essential to the unfolding approach. As a result,our new LFS method computes a reduced transition system without the problem of state duplication (present in the original LFS). Since it works for any transition system with an independence relation,this black box partial unfolding remains more general than the unfolding of Petri nets. Experiments show that the combination gives improved reductions compared to the original LFS.

Regular Sets of Pomsets with Autoconcurrency

Partially ordered multisets (or pomsets) constitute one of the most basic models of concurrency. We introduce and compare several notions of regularity for pomset languages by means of contexts and residues of different kinds. We establish some interesting closure properties that allow us to relate this approach to SP-recognizability in the particular case of series-parallel pomsets. Finally we introduce the framework of compatible languages which generalizes several classical formalisms (including message sequence charts and firing pomsets of Petri nets). In this way, we identify regular sets of pomsets as recognizable subsets in the monoid of multiset sequences.

The synthesis problem of netcharts

A netchart is basically a Petri net whose places are located at some process and whose transitions are labeled by message sequence charts (MSCs). Two recent papers showed independently that any globally-cooperative high-level MSC corresponds to the behaviors of some communicating finite-state machine — or equivalently a netchart. These difficult results rely either on Thomas’ graph acceptors or Zielonka’s construction of asynchronous automata. In this paper we give a direct and self-contained synthesis of netcharts from globally-cooperative high-level MSCs by means of a simpler unfolding procedure.