On (Omega-)regular model checking

peer reviewedChecking infinite-state systems is frequently done by encoding infinite sets of states as regular languages. Computing such a regular representation of, say, the set of reachable states of a system requires acceleration techniques that can finitely compute the effect of an unbounded number of transitions. Among the acceleration techniques that have been proposed, one finds both specific and generic techniques. Specific techniques exploit the particular type of system being analyzed, for example, a system manipulating queues or integers, whereas generic techniques only assume that the transition relation is represented by a finite-state transducer, which has to be iterated. In this article, we investigate the possibility of using generic techniques in cases where only specific techniques have been exploited so far. Finding that existing generic techniques are often not applicable in cases easily handled by specific techniques, we have developed a new approach to iterating transducers. This new approach builds on earlier work, but exploits a number of new conceptual and algorithmic ideas, often induced with the help of experiments, that give it a broad scope, as well as good performances

Towards Statistical Prioritization for Software Product Lines Testing

Software Product Lines (SPL) are inherently difficult to test due to the combinatorial explosion of the number of products to consider. To reduce the number of products to test, sampling techniques such as combinatorial interaction testing have been proposed. They usually start from a feature model and apply a coverage criterion (e.g. pairwise feature interaction or dissimilarity) to generate tractable, fault-finding, lists of configurations to be tested. Prioritization can also be used to sort/generate such lists, optimizing coverage criteria or weights assigned to features. However, current sampling/prioritization techniques barely take product behavior into account. We explore how ideas of statistical testing, based on a usage model (a Markov chain), can be used to extract configurations of interest according to the likelihood of their executions. These executions are gathered in featured transition systems, compact representation of SPL behavior. We discuss possible scenarios and give a prioritization procedure illustrated on an example.Comment: Extended version published at VaMoS '14 (http://dx.doi.org/10.1145/2556624.2556635

Verification of interlocking systems using statistical model checking

In the railway domain, an interlocking is the system ensuring safe train traffic inside a station by controlling its active elements such as the signals or points. Modern interlockings are configured using particular data, called application data, reflecting the track layout and defining the actions that the interlocking can take. The safety of the train traffic relies thereby on application data correctness, errors inside them can cause safety issues such as derailments or collisions. Given the high level of safety required by such a system, its verification is a critical concern. In addition to the safety, an interlocking must also ensure that availability properties, stating that no train would be stopped forever in a station, are satisfied. Most of the research dealing with this verification relies on model checking. However, due to the state space explosion problem, this approach does not scale for large stations. More recently, a discrete event simulation approach limiting the verification to a set of likely scenarios, was proposed. The simulation enables the verification of larger stations, but with no proof that all the interesting scenarios are covered by the simulation. In this paper, we apply an intermediate statistical model checking approach, offering both the advantages of model checking and simulation. Even if exhaustiveness is not obtained, statistical model checking evaluates with a parametrizable confidence the reliability and the availability of the entire system.Comment: 12 pages, 3 figures, 2 table

Étude de l'influence de défauts sur les propriétés mécaniques de matériaux composites fabriqués par le procédé de placement de fibres

RÉSUMÉ Les gaps et overlaps, défauts provoqués par le procédé de placement de fibres automatisé, ont un effet peu connu sur les propriétés mécaniques des matériaux composites. La réponse à l’impact et la tenue en compression du matériau sont susceptibles d’être affectées par ces défauts. Ce mémoire présente l’étude de l’effet de ces défauts sur les propriétés à l’impact (ASTM D7136), en compression après impact (ASTM D7137) et en open hole compression (ASTM D6484) d’un laminé quasi-isotrope carbone/époxy (G40-800/5276-1). Les défauts étudiés sont « critiques » car ils sont placés dans tous les plis de même orientation du laminé et superposés les uns au dessus des autres. Dans un premier temps nous avons réalisé des tests de open hole compression sur des éprouvettes contenant des défauts. 7 configurations de défauts, des gaps et des overlaps placés dans le sens de la compression ou perpendiculairement à la compression, ont été comparées aux échantillons sans défauts. Les résultats de ces tests, comparés à une modélisation analytique, montrent que les défauts placés dans la direction de la compression ne provoquent pas de concentrations de contraintes à l’origine de la rupture des éprouvettes. L’effet des défauts sur la résistance en compression du matériau est faible et prévisible. Les défauts placés à 90° par rapport au chargement provoquent une plus forte réduction des propriétés en compression du matériau, due à l’effet de fiber waviness. Cependant, des observations au microscope électronique ont montré que le fiber waviness touche principalement les plis adjacents aux défauts (+/-45°) et non les plis à 0°, porteurs de la plupart de la charge, ce qui explique que la diminution de résistance reste relativement faible. Nous avons ensuite réalisé des tests d’impact et de compression après impact. En plus des données directes des tests d’impact (force de contact de l’impacteur et énergie absorbée au cours de l’impact), nous avons effectué des mesures à l’aide d’un scanner à ultrasons (C-scan) et des observations au microscope électronique qui nous ont permis de déterminer les dommages provoqués par l’impact sur le laminé. Dans un premier temps nous avons étudié les modes d’endommagement du laminé en fonction de l’énergie d’impact. Pour les plus faibles énergies d’impact le laminé ne présente aucun dommage. Ensuite, lorsque l’énergie augmente, des fissurations de la matrice apparaissent suivies des délaminations, puis des première ruptures de fibres. Le dommage s’étend alors dans les plis du laminé opposés au point d’impact.----------ABSTRACT The effect of automated fiber placement defects on composite material mechanical properties needs to be characterized. Impact behavior and laminate compressive properties can be affected by these defects. This study aims at characterizing the effect of AFP defects on impact (ASTM D7136), compression after impact (ASTM D7137) and open hole compression properties (ASTM D6484) of a quasi-isotropic carbon/epoxy laminate (G40-800/5276-1). The defects that we studied were “critical” because they were located in every plies of same orientation and they were stacked. First, we performed open hole compression tests on coupons containing defects. 7 defect configurations were studied with gaps and overlaps placed in the compression direction and perpendicular to the compression direction. The results are compared with an analytical modeling of defects and they reveal that if defects are placed along compression direction they do not cause stress concentrations which lead to specimen failure. If defects are placed in plies which are perpendicular to compression direction, fiber waviness leads to a more important reduction of compressive strength. But electron microscope observations revealed that fiber waviness only affect plies that are adjacent to defects (+/-45°) and do not affect 0° plies which carry most of the load. It explains that compressive strength reduction is low even for 90° defects. Then we performed impact and compression after impact tests. We studied the results of impact tests (impactor contact force and impact absorbed energy) and we also performed ultrasonic measures (C-scan) and electron microscope observations, it allowed us to characterize impact damages. We first studied the effect of impact energy on laminate damage modes. For lower impact energies there is no damage in the material. When the impact energy increases, matrix cracking and délaminations appear, they are followed by the first fiber fractures. The damage spreads in plies which are opposed to the impact point. For higher energies, material properties are highly reduced and the laminate cannot support the load increase, the damage propagates through the laminate thickness. Finally impact and compression after impact tests performed on coupons containing defects reveal that gaps and overlaps have a local effect on damage: defects do not affect coupons global mechanical properties