Verification methods for behavioural specifications
Méthodes de vérification de spécifications comportementales : étude et mise en œuvre
Résumé
This work deals with the verification of behavioural specifications for parallel programs, and, more precisely, with the design of efficient algorithms for the comparison of two labelled transition systems modulo a simulation or a bisimulation relation. First, we recall the principle of the classical decision procedures, based on partition refinement algorithms. This approach requires to previously build the transition relations of the two systems before the comparison phase, which constitutes a practical limitation. Consequently, we propose an original algorithm, based on a depth-first traversal of a synchronous product of the two systems, which allows to perform the comparison ``on the fly'', without explicitly building or storing the two transition relations. This ``on the fly'' comparison algorithm has been implemented within the Aldebaran verification tool with for various relations: strong bisimulation, observational equivalence, tau*a-bisimulation, delay bisimulation and branching bisimulation, as well as safety equivalence and preorder. Its application to the verification of several Lotos programs confirms the interest of this approach in comparison with the more classical ones. Finally, we are also concerned with diagnostic generation when the two labelled transitions systems are not equivalent: the decision procedures implemented within Aldebaran provide a set of discriminating execution sequences, which are minimal with respect to a given order relation.
Nous rappelons tout d'abord le principe des procedures de decision classiques,qui reposent sur des algorithmes de raffinement de partitions. Cette approche necessite de construire au prealable les relations de transition des deux systemes a comparer, ce qui constitue une limitation en pratique. Nous proposons par consequent un algorithme original, base sur un parcours en profondeur du produit synchrone des deux systèmes, qui permet d'effectuer la comparaison ``a la volee'', sans jamais construire ni mémoriser explicitementles deux relations de transition. L'algorithme de comparaison ``a la volée'' a ete mis en œuvre au sein du logiciel de verification Aldebaran dans le cas de différentes relations : la bisimulation forte, l'équivalence observationnelle, la tau*a-bisimulation, la delay bisimulation et la bisimulation de branchement, ainsi que le preordre et l'equivalence de surete. Son application a la verification de plusieurs programmes Lotos de taille realiste a confirme l'interet pratique de notre approche par rapport aux methodes classiques. Enfin, nous nous interessons egalement a la generation d'un diagnostic lorsque les deux systemes de transitions etiquetees a comparer ne sont pas equivalents : les procedures de decision implementees dans Aldebaran fournissent le cas echeant un ensemble de sequences d'execution discriminantes, minimales pour une relation d'ordre donnee.
Domaines
Génie logiciel [cs.SE]
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