Connector algebras for C/E and P/T nets interactions

A quite fourishing research thread in the recent literature on component based system is concerned with the algebraic properties of different classes of connectors. In a recent paper, an algebra of stateless connectors was presented that consists of five kinds of basic connectors, namely symmetry, synchronization, mutual exclusion, hiding and inaction, plus their duals and it was shown how they can be freely composed in series and in parallel to model sophisticated "glues". In this paper we explore the expressiveness of stateful connectors obtained by adding one-place buffers or unbounded buffers to the stateless connectors. The main results are: i) we show how different classes of connectors exactly correspond to suitable classes of Petri nets equipped with compositional interfaces, called nets with boundaries; ii) we show that the difference between strong and weak semantics in stateful connectors is reflected in the semantics of nets with boundaries by moving from the classic step semantics (strong case) to a novel banking semantics (weak case), where a step can be executed by taking some "debit" tokens to be given back during the same step; iii) we show that the corresponding bisimilarities are congruences (w.r.t. composition of connectors in series and in parallel); iv) we show that suitable monoidality laws, like those arising when representing stateful connectors in the tile model, can nicely capture concurrency aspects; and v) as a side result, we provide a basic algebra, with a finite set of symbols, out of which we can compose all P/T nets, fulfilling a long standing quest

Mapping RT-LOTOS specifications into Time Petri Nets

RT-LOTOS is a timed process algebra which enables compact and abstract specification of real-time systems. This paper proposes and illustrates a structural translation of RT-LOTOS terms into behaviorally equivalent (timed bisimilar) finite Time Petri nets. It is therefore possible to apply Time Petri nets verification techniques to the profit of RT-LOTOS. Our approach has been implemented in RTL2TPN, a prototype tool which takes as input an RT-LOTOS specification and outputs a TPN. The latter is verified using TINA, a TPN analyzer developed by LAAS-CNRS. The toolkit made of RTL2TPN and TINA has been positively benchmarked against previously developed RT-LOTOS verification tool

Effective representation of RT-LOTOS terms by finite time petri nets

The paper describes a transformational approach for the specification and formal verification of concurrent and real-time systems. At upper level, one system is specified using the timed process algebra RT-LOTOS. The output of the proposed transformation is a Time Petri net (TPN). The paper particularly shows how a TPN can be automatically constructed from an RT-LOTOS specification using a compositionally defined mapping. The proof of the translation consistency is sketched in the paper and developed in [1]. The RT-LOTOS to TPN translation patterns formalized in the paper are being implemented. in a prototype tool. This enables reusing TPNs verification techniques and tools for the profit of RT-LOTOS

A Decidable Characterization of a Graphical Pi-calculus with Iterators

This paper presents the Pi-graphs, a visual paradigm for the modelling and verification of mobile systems. The language is a graphical variant of the Pi-calculus with iterators to express non-terminating behaviors. The operational semantics of Pi-graphs use ground notions of labelled transition and bisimulation, which means standard verification techniques can be applied. We show that bisimilarity is decidable for the proposed semantics, a result obtained thanks to an original notion of causal clock as well as the automatic garbage collection of unused names.Comment: In Proceedings INFINITY 2010, arXiv:1010.611

Slimming down Petri Boxes: Compact Petri Net Models of Control Flows

We look at the construction of compact Petri net models corresponding to process algebra expressions supporting sequential, choice, and parallel compositions. If "silent" transitions are disallowed, a construction based on Cartesian product is traditionally used to construct places in the target Petri net, resulting in an exponential explosion in the net size. We demonstrate that this exponential explosion can be avoided, by developing a link between this construction problem and the problem of finding an edge clique cover of a graph that is guaranteed to be complement-reducible (i.e., a cograph). It turns out that the exponential number of places created by the Cartesian product construction can be reduced down to polynomial (quadratic) even in the worst case, and to logarithmic in the best (non-degraded) case. As these results affect the "core" modelling techniques based on Petri nets, eliminating a source of an exponential explosion, we hope they will have applications in Petri net modelling and translations of various formalisms to Petri nets

Characterizing Behavioural Congruences for Petri Nets

We exploit a notion of interface for Petri nets in order to design a set of net combinators. For such a calculus of nets, we focus on the behavioural congruences arising from four simple notions of behaviour, viz., traces, maximal traces, step, and maximal step traces, and from the corresponding four notions of bisimulation, viz., weak and weak step bisimulation and their maximal versions. We characterize such congruences via universal contexts and via games, providing in such a way an understanding of their discerning powers

Extending the Petri box calculus with time

PBC (Petri Box Calculus) is a process algebra where real parallelism of concurrent systems can be naturally expressed. One of its main features is the definition of a denotational semantics based on Petri nets, which emphasizes the structural aspects of the modelled systems. However, this formal model does not include temporal aspects of processes, which are necessary when considering real-time systems. The aim of this paper is to extend the existing calculus with those temporal aspects. We consider that actions are not instantaneous, that is, their execution takes time. We present an operational semantics and a denotational semantics based on timed Petri nets. Finally, we discuss the introduction of other new features such as time-outs and delays. Throughout the paper we assume that the reader is familiar with both Petri nets and PBC