Franck Pommereau

Asynchronous Links in the PBC and M-Nets

This paper aims at introducing an extension of M-nets, a fully compositional class of high-level Petri nets, and of its low-level counter part, Petri Boxes Calculus (PBC). We introduce a new operator with nice algebraic properties which allows to express asynchronous communications in a simple and flexible way. With this extension, asynchronous communications become at least as simple to express as (existing) synchronous ones. Finally, we show how this extension can be used in order to specify systems with timing constraints.

Petri nets with causal time for system verification

We present a new approach to the modelling of time constrained systems. It is based on untimed high-level Petri nets using the concept of causal time. With this concept, the progression of time is modelled in the system by the occurrence of a distinguished event, tick, which serves as a reference to the rest of the system. In order to validate this approach as suitable for automated verification, a case study is provided and the results obtained using a model-checker on high-level Petri nets are compared with those obtained for timed automata using prominent tools. The comparison is encouraging and shows that the causal time approach is intuitive and modular. It also potentially allows for efficient verification.

Modeling and Analysis of Security Protocols Using Role Based Specifications and Petri Nets

In this paper, we introduce a framework composed of a syntax and its compositional Petri net semantics, for the specification and verification of properties (like authentication) of security protocols. The protocol agents (e.g., an initiator, a responder, a server, a trusted third party, ...) are formalized as roles, each of them having a predefined behavior depending on their global and also local knowledge (including for instance public, private and shared keys), and may interact in a potentially hostile environment. The main characteristics of our framework, is that it makes explicit, structured and formal, the usually implicit information necessary to analyse the protocol, for instance the public and private contextof execution. The roles and the environment are expressed using SPL processes and compositionally translated into high-level Petri nets, while the context specifying the global and local knowledge of the participants in the protocol is used to generate the corresponding initial marking (with respect to the studied property). Finally, this representation is used to analyse the protocol properties, applying techniques of simulation and model-checking on Petri nets. The complete approach is illustrated on the case study of the Kao-Chow authentication protocol.

Modelling, verification, and formal analysis of security properties in a P2P system

We present a security analysis of the SPREADS1 system, a distributed storage service based on a centralized peer-to-peer architecture. We formally modelled the salient behavior of the actual system using ABCD, a high level specification language with a coloured Petri net semantics, which allowed the execution states of the system to be verified. We verified the behavior of the system in the presence of an external Dolev-Yao attacker, unearthing some replay attacks in the original system. Furthermore, since the implementation is also a formal model, we have been able to show that any execution of the model satisfies certain desirable security properties once these flaws are repaired.

A Concurrent and Compositional Petri Net Semantics of Preemption

The aim of this paper is the introduction of preemption in a compositional model, called M-nets, which is based on Petri nets and hence provided with a concurrent semantics. We propose a way to model preemptible systems by extending the M-net model with priorities and the M-net algebra with a preemption operator. We show that these extensions can be seen as a high-level version of the well studied model of priority systems, and so, can be reduced to Petri nets (without priorities) which retain as much as possible of the original concurrency. As a consequence, Petri nets appear as a model powerful enough to deal with preemption in a compositional way and with a concurrent semantics.

M-nets: a survey

This paper surveys the research related to the model of M-nets since it was introduced in 1995. M-nets are high-level labelled Petri nets which can be composed, like process algebra terms, using various operators. We present the core model, several of its extensions and the main applications.

A Concurrent Semantics of Static Exceptions in a Parallel Programming Language

This paper aims at introducing a mechanism of exceptions in a parallel programming language, giving them a formal concurrent semantics in terms of preemptible and composable high-level Petri nets. We show that, combined with concurrency, exceptions can be used as a basis for other preemption related constructs. We illustrate this idea by presenting a generalized timeout and a simple UNIX-like system of concurrent preemptible threads.

SNAKES: A Flexible High-Level Petri Nets Library (Tool Paper)

SNAKES (SNAKES is the Net Algebra Kit for Editors and Simulators) is a general purpose Petri nets library, primarily for the Python programming language but portable to other ones. It defines a very general variant of Python-coloured Petri nets that can be created and manipulated through the library, as well as executed to explore state spaces. Thanks to a variety of plugins, SNAKES can handle extensions of Petri nets, in particular algebras of Petri nets [4, 26]. SNAKES ships with a compiler for the ABCD language that is precisely such an algebra. Finally, one can use the companion tool Neco [14] that compiles a Petri net into an optimised library allowing to compute efficiently its state space or perform LTL model-checking thanks to library SPOT [8, 13]. This paper describes SNAKES’ structure and features.

Causal Time Calculus

We present a process algebra suitable to the modelling of timed concurrent systems and to their efficient verification through model checking. The algebra is provided with two consistent semantics: a structural operational semantics (as usual for process algebras) and a denotational semantics in terms of Petri nets in which time is introduced through counters of explicit clock ticks. This way of modelling time has been called causal time so the process algebra is itself called the Causal Time Calculus (CTC). It was shown in a separate paper that the causal time approach allowed for efficient verification but suffered from a sensitivity to the constants to which counts of ticks are compared. We show in this paper how this weakness can be removed.

A Modular, Qualitative Modeling of Regulatory Networks Using Petri Nets

Advances in high-throughput technologies have enabled the delineation of large networks of interactions that control cellular processes. To understand behavioral properties of these complex networks, mathematical and computational tools are required. The multi-valued logical formalism, initially defined by Thomas and coworkers, proved well adapted to account for the qualitative knowledge available on regulatory interactions, and also to perform analyses of their dynamical properties. In this context, we present two representations of logical models in terms of Petri nets. In a first step, we briefly show how logical models of regulatory networks can be transposed into standard (place/transition) Petri nets, and discuss the capabilities of such a representation. In the second part, we focus on logical regulatory modules and their composition, demonstrating that a high-level Petri net representation greatly facilitates the modeling of interconnected modules. Doing so, we introduce an explicit means to integrate signals from various interconnected modules, taking into account their spatial distribution. This provides a flexible modeling framework to handle regulatory networks that operate at both intra- and intercellular levels. As an illustration, we describe a simplified model of the segment-polarity module involved in the segmentation of the Drosophila embryo.