Maximilien Colange

Report on the Model Checking Contest at Petri Nets 2011

This article presents the results of the Model Checking Contest held within the SUMo 2011 workshop, a satellite event of Petri Nets 2011. This contest aimed at a fair and experimental evaluation of the performances of model checking techniques applied to Petri nets.

Crocodile: a symbolic/symbolic tool for the analysis of symmetric nets with bag

The use of high-level nets, such as colored Petri nets, is very convenient for modeling complex systems in order to have a compact, readable and structured specification. Symmetric Nets with Bags (SNB) were introduced to cope with this goal without introducing a burden due to the underlying complexity of the state space. The structure of bags allows through exploitation of symmetries to provide a compact quotient state space representation (similarly to the construction proposed in GreatSPN). In this paper, we present Crocodile, the first implementation of a modeling environment and model checker dedicated to SNB. Its goal is first to be a proof of concept for experimenting the quotient graph techniques together with hierarchical set decision diagrams. A second objective is to enable experimentation of modeling techniques with this new class of Petri nets.

Towards Distributed Software Model-Checking Using Decision Diagrams

Symbolic data structures such as Decision Diagrams have proved successful for model-checking. For high-level specifications such as those used in programming languages, especially when manipulating pointers or arrays, building and evaluating the transition is a challenging problem that limits wider applicability of symbolic methods. We propose a new symbolic algorithm, EquivSplit, allowing an efficient and fully symbolic manipulation of transition relations on Data Decision Diagrams. It allows to work with equivalence classes of states rather than individual states. Experimental evidence on the concurrent software oriented benchmark BEEM shows that this approach is competitive.

StrataGEM: A Generic Petri Net Verification Framework

In this paperwe present the Strategy Generic Extensible Modelchecker (StrataGEM), a tool aimed at the analysis of Petri nets and other models of concurrency by means of symbolic model-checking techniques. StrataGEM marries the well know concepts of Term Rewriting (TR) to the efficiency of Decision Diagrams (DDs). TR systems are a great way to describe the semantics of a system, being readable and compact, but their direct implementation tends to be rather slow on large sets of terms. On the other hand, DDs have demonstrated their efficiency for model-checking, but translating a system semantics into efficient DDs operations is an expert’s matter. StrataGEM describes the semantics of a system in terms of strategies over a TR system, and automatically translates these rules into operations on DD to handle the model-checking. The ultimate goal of StrataGEM is to become a verification framework for the different variants of Petri nets by separating the semantics of the model from the computation that performs model-checking.

Symbolic Optimal Reachability in Weighted Timed Automata

Weighted timed automata have been defined in the early 2000 s for modelling resource-consumption or -allocation problems in real-time systems. Optimal reachability is decidable in weighted timed automata, and a symbolic forward algorithm has been developed to solve that problem. This algorithm uses so-called priced zones, an extension of standard zones with cost functions. In order to ensure termination, the algorithm requires clocks to be bounded. For unpriced timed automata, much work has been done to develop sound abstractions adapted to the forward exploration of timed automata, ensuring termination of the model-checking algorithm without bounding the clocks. In this paper, we take advantage of recent developments on abstractions for timed automata, and propose an algorithm allowing for symbolic analysis of all weighted timed automata, without requiring bounded clocks.

State Space Analysis Using Symmetries on Decision Diagrams

Two well-accepted techniques to tackle combinatorial explosion in model-checking are exploitation of symmetries and the use of reduced decision diagrams. Some work showed that these two techniques can be stacked in specific cases. This paper presents a novel and more general approach to combine these two techniques. Expected benefits of this combination are:· in symmetry-based reduction, the main source of complexity resides in the canonization computation that must be performed for each new encountered state, the use of shared decision diagrams allows one to canonize sets of states at once.· in decision diagram based techniques, dependencies between variables induce explosion in representation size, the manipulation of canonical states allows to partly overcome this limitation. We show that this combination is experimentally effective in many typical cases.

The 4th reactive synthesis competition (SYNTCOMP 2017): Benchmarks, participants & results

We report on the fourth reactive synthesis competition (SYNTCOMP 2017). We introduce two new benchmark classes that have been added to the SYNTCOMP library, and briefly describe the benchmark selection, evaluation scheme and the experimental setup of SYNTCOMP 2017. We present the participants of SYNTCOMP 2017, with a focus on changes with respect to the previous years and on the two completely new tools that have entered the competition. Finally, we present and analyze the results of our experimental evaluation, including a ranking of tools with respect to quantity and quality of solutions.

Building a Symbolic Model Checker from Formal Language Description

The main limit towards practical model-checking is the combinatorial explosion of the number of states. Among numerous solutions proposed to tackle this problem, Decision Diagrams (DDs) have been proved efficient. They are however low-level data structures: translating a high-level model to them can be cumbersome. Indeed, little work towards their better usability has been undertaken. We propose an abstract mechanism for the manipulation of DDs, where system transitions are described in terms of rewrite rules. We describe how basic rewrite rules can be assembled through strategies, to describe complex transition relations (e.g. involving various levels of synchronization among parallel components). The strategies and rewrite rules offer a higher-level interface, where the nature of underlying DD is hidden, close to high-level languages used to model concurrent systems. We also describe specific strategies that we use to automatically translate high-level modeling languages (namely Petri Nets and imperative languages) to rewrite strategies, ultimately translated in terms of operations on DDs.

Extreme symmetries in complex distributed systems: the bag-oriented approach

Model checking is widely used as an automatic exhaustive verification technique to check properties of complex systems. However, it is difficult to operate in the context of todays emerging systems that combine distribution (and asynchronous communications) together with a large size (and a hierarchical composition of components --- and thus, of specifications). This paper combines existing techniques tackling the known combinatorial explosion of model checking. To achieve this, we exploit the structure of such distributed systems (symmetries and hierarchical composition), thus allowing a better compression factor and calculus factorization in favorable cases. We present these techniques and assess their impact on some benchmark examples.

CDCLSym: Introducing Effective Symmetry Breaking in SAT Solving

SAT solvers are now widely used to solve a large variety of problems, including formal verification of systems. SAT problems derived from such applications often exhibit symmetry properties that could be exploited to speed up their solving. Static symmetry breaking is so far the most popular approach to take advantage of symmetries. It relies on a symmetry preprocessor which augments the initial problem with constraints that force the solver to consider only a few configurations among the many symmetric ones.