Denis Poitrenaud

SPOT: an extensible model checking library using transition-based generalized Bu/spl uml/chi automata

SPOT (SPOT produces our traces), is a C++ library offering model checking bricks that can be combined and interfaced with third party tools to build a model checker. It relies on transition-based generalized Bu/spl uml/chi automata (TGBA) and does not need to degeneralize these automata to check their emptiness. We motivate the choice of TGBA by illustrating a very simple (yet efficient) translation of LTL (linear temporal logic) into TGBA. We then show how it supports on-the-fly computations, and how it can be extended or integrated in other tools.

On-the-fly emptiness checks for generalized büchi automata

Emptiness check is a key operation in the automata-theoretic approach to LTL verification. However, it is usually done on Buchi automata with a single acceptance condition. We review existing on-the-fly emptiness-check algorithms for generalized Buchi automata (i.e., with multiple acceptance conditions) and show how they compete favorably with emptiness-checks for degeneralized automata, especially in presence of weak fairness assumptions. We also introduce a new emptiness-check algorithm, some heuristics to improve existing checks, and propose algorithms to compute accepting runs in the case of multiple acceptance conditions.

Theoretical Aspects of Recursive Petri Nets

The model of recursive Petri nets (RPNs) has been introduced in the field of multi-agent systems in order to model flexible plans for agents. In this paper we focus on some theoretical aspects of RPNs. More precisely, we show that this model is a strict extension of the model of Petri nets in the following sense : the family of languages of RPNs strictly includes the union of Petri net and Context Free languages. Then we prove the main result of this work, the decidability of the reachability problem for RPNs.

Recursive Petri nets: Theory and application to discrete event systems

In order to design and analyse complex systems, modelers need formal models with two contradictory requirements: a high expressivity and the decidability of behavioural property checking. Here we present and develop the theory of such a model, the recursive Petri nets. First, we show that the mechanisms supported by recursive Petri nets enable to model patterns of discrete event systems related to the dynamic structure of processes. Furthermore, we prove that these patterns cannot be modelled by ordinary Petri nets. Then we study the decidability of some problems: reachability, finiteness and bisimulation. At last, we develop the concept of linear invariants for this kind of nets and we design efficient computations specifically tailored to take advantage of their structure.

Hierarchical Set Decision Diagrams and Regular Models

This paper presents algorithms and data structures that exploit a compositional and hierarchical specification to enable more efficient symbolic model-checking. We encode the state space and transition relation using hierarchical Set Decision Diagrams (SDD) [9].In SDD, arcs of the structure are labeled with sets, themselves stored as SDD. To exploit the hierarchy of SDD, a structured model representation is needed. We thus introduce a formalism integrating a simple notion of type and instance . Complex composite behaviors are obtained using a synchronization mechanism borrowed from process calculi. Using this relatively general framework, we investigate how to capture similarities in regular and concurrent models. Experimental results are presented, showing that this approach can outperform in time and memory previous work in this area.

A Symbolic Symbolic State Space Representation

Symmetry based approaches are known to attack the state space explosion problem encountered during the analysis of distributed systems. In another way, BDD-like encodings enable the management of huge data sets. In this paper, we show how to benefit from both approaches automatically. Hence, a quotient set is built from a coloured Petri net description modeling the system. The reachability set is managed under some explicit symbolic operations. Also, data representations are managed symbolically based on a recently introduced data structure, called Data Decisions Diagrams, that allow flexible definition of application specific operators. Performances yielded by our prototype are reported in the paper.

Modelling and Analyzing Systems with Recursive Petri Nets

Recursive Petri nets (RPNs) have been introduced to model systems with dynamic structure. In a previous work, we have shown that this model is a strict extension of Petri nets, whereas reachability in RPNs remains decidable. Here, we focus on its modelling features and on some additional theoretical aspects. Three different kinds of discrete event systems are modellized by RPNs in order to give an insight of their capabilities to express various mechanisms. Decision procedures for new properties like boundedness and fmiteness are presented and recursiveness of languages of RPNs is proved. At last, we compare RPNs with two other models combining Petri nets and context-free grammars features showing that these models can be simulated by RPNs.

Self-loop aggregation product: a new hybrid approach to on-the-fly LTL model checking

We present the Self-Loop Aggregation Product (SLAP), a new hybrid technique that replaces the synchronized product used in the automata-theoretic approach for LTL model checking. The proposed product is an explicit graph of aggregates (symbolic sets of states) that can be interpreted as a Buchi automaton. The criterion used by SLAP to aggregate states from the Kripke structure is based on the analysis of self-loops that occur in the Buchi automaton expressing the property to verify. Our hybrid approach allows on the one hand to use classical emptiness-check algorithms and build the graph on-the-fly, and on the other hand, to have a compact encoding of the state space thanks to the symbolic representation of the aggregates. Our experiments show that this technique often outperforms other existing (hybrid or fully symbolic) approaches.

Three SCC-Based Emptiness Checks for Generalized Büchi Automata

The automata-theoretic approach for the verification of linear time properties involves checking the emptiness of a Buchi automaton. However generalized Buchi automata, with multiple acceptance sets, are preferred when verifying under weak fairness hypotheses. Existing emptiness checks for which the complexity is independent of the number of acceptance sets are all based on the enumeration of Strongly Connected Components (SCCs).

Pre-and post-gglomerations for LTL model checking

One of the most efficient analysis technique is to reduce an original model into a simpler one such that the reduced model has the same properties than the original one. G. Berthelot defined in this thesis some reductions of Petri nets that are based on local structural conditions and that simplify significantly the net. However, the author focused only on the preservation of classical properties (such that liveness, boundedness, ...) that are not necessarily the most useful in practice. In this paper, we prove that two of these structural reductions (the pre and post transitions agglomerations) preserve also a large set of properties expressed in linear-time temporal logics under simple conditions.