49 research outputs found
Compilation de CSPs : carte de complexité des MDDs non-déterministes
National audienceLes CSPs fournissent un cadre puissant pour la reprĂ©sentation de problĂšmes trĂšs divers. La difficultĂ© est que la plupart des requĂȘtes associĂ©es aux CSPs sont NP-difficiles, mais doivent dans certains contextes ĂȘtre traitĂ©es « en ligne ». Câest pour cette raison que les diagrammes de dĂ©cision multivaluĂ©s (MDDs) ont Ă©tĂ© proposĂ©s pour la compilation de CSPs. Cet article dresse une carte de compilation des MDDs, dans lâesprit de la carte de la famille des NNFs de Darwiche et Marquis, en analysant les MDDs selon leur compacitĂ© et les requĂȘtes et transformations quâils supportent en temps polynomial. Les MDDs dĂ©terministes et ordonnĂ©s gĂ©nĂ©ralisant les diagrammes de dĂ©cision binaire ordonnes Ă des variables non-boolĂ©ennes, le fait que leurs propriĂ©tĂ©s soient similaires nâest pas surprenant. Cependant, notre Ă©tude met en avant lâintĂ©rĂȘt des MDDs ordonnes non dĂ©terministes : restreint aux variables boolĂ©ennes, ce fragment est strictement plus compact que ceux des OBDDs et des DNFs, et admet des performances proches de celles des DNNFs. La comparaison aux MDDs classiques montre que relĂącher la contrainte du dĂ©terminisme amĂ©liore la compacitĂ© et permet a plus de transformations dâĂȘtre supportĂ©es en temps polynomial. Des expĂ©riences sur des problĂšmes alĂ©atoires confirment le gain en compacitĂ©
Structural model checking
The introduction of symbolic approaches, based on Binary Decision Diagrams (BDD), to Model Checking has led to significant improvements in Formal Verification, by allowing the analysis of very large systems, such as complex circuit designs. These were previously beyond the reach of traditional, explicit methods, due to the state space explosion phenomenon. However, after the initial success, the BDD technology has peaked, due to a similar problem, the BDD explosion.;We present a new approach to symbolic Model Checking that is based on exploiting the system structure. This technique is characterized by several unique features, including an encoding of states with Multiway Decision Diagrams (MDD) and of transitions with boolean Kronecker matrices. This approach naturally captures the property of event locality, inherently present in the class of globally asynchronous/locally synchronous systems.;The most important contribution of our work is the saturation algorithm for state space construction. Using saturation, the peak size of the MDD (luring the exploration is drastically reduced, often to sizes equal or comparable to the final MDD size, which makes it optimal in these terms. Subsequently, saturation can achieve similar reductions in runtimes. When compared to the leading state-of-the art tools based on traditional symbolic approaches, saturation is up to 100,000 times faster and uses up to 1,000 times less memory. This enables our approach to study much larger systems than ever considered. Following the success in state space exploration, we extend the applicability of the saturation algorithm to CTL Model Checking, and also to efficient generation of shortest length counterexamples for safety properties, with similar results.;This approach to automatic verification is implemented in the tool SMART. We test the new model checker on a real life, industrial size application: the NASA Runway Safety Monitor (RSM). The analysis exposes a number of potential problems with the decision procedure designed to signal all hazardous situations during takeoff and landing procedures on runways. Attempts to verify RSM with other model checkers (NuSMV, SPIN) fail due to excessive memory consumption, showing that our structural method is superior to existing symbolic approaches
Vers une carte de compilation pour des langages de représentation hétérogÚnes
National audienceLa carte de compilation introduite par Darwiche et Marquis sâappuie sur divers concepts (principalement ceux de requËete, transformation, expressivit Ìe et conci- sion) pour comparer la relative ad Ìequation des langages de repr Ìesentation `a certains probl`emes dâIA. Cependant,ce cadre est limit Ìe `a la comparaison de langages inter- pr Ìet Ìes de mani`ere homog`ene (les formules sont interpr Ìe- t Ìees comme des fonctions bool Ìeennes). Cela empËeche lacomparaison formelle entre des langages pourtant essen- tiellement proches, tels que ceux des OBDDs, MDDs et ADDs. Pour combler cette lacune, cet article pr Ìesente un cadre g Ìen Ìeralis Ìe dans lequel la comparaison formelle de langages de repr Ìesentation h Ìet Ìerog`enes devient fai-sable. En particulier, il explique comment les notions- clefs de requËete, transformation, expressivit Ìe et concision peuvent sâadapter au formalisme g Ìen Ìeralis Ì