Showing papers by "Jean-François Raskin published in 2008"

Robust safety of timed automata

Abstract: Timed automata are governed by an idealized semantics that assumes a perfectly precise behavior of the clocks. The traditional semantics is not robust because the slightest perturbation in the timing of actions may lead to completely different behaviors of the automaton. Following several recent works, we consider a relaxation of this semantics, in which guards on transitions are widened by Δ>0 and clocks can drift by ?>0. The relaxed semantics encompasses the imprecisions that are inevitably present in an implementation of a timed automaton, due to the finite precision of digital clocks. We solve the safety verification problem for this robust semantics: given a timed automaton and a set of bad states, our algorithm decides if there exist positive values for the parameters Δ and ? such that the timed automaton never enters the bad states under the relaxed semantics.

Antichains: alternative algorithms for LTL satisfiability and model-checking

Abstract: The linear temporal logic (LTL) was introduced by Pnueli as a logic to express properties over the computations of reactive systems Since this seminal work, there have been a large number of papers that have studied deductive systems and algorithmic methods to reason about the correctness of reactive programs with regard to LTL properties In this paper, we propose new efficient algorithms for LTL satisfiability and model-checking Our algorithms do not construct nondeterministic automata from LTL formulas but work directly with alternating automata using efficient exploration techniques based on antichains

Equivalence of labeled Markov chains

Abstract: We consider the equivalence problem for labeled Markov chains (LMCs), where each state is labeled with an observation. Two LMCs are equivalent if every finite sequence of observations has the same probability of occurrence in the two LMCs. We show that equivalence can be decided in polynomial time, using a reduction to the equivalence problem for probabilistic automata, which is known to be solvable in polynomial time. We provide an alternative algorithm to solve the equivalence problem, which is based on a new definition of bisimulation for probabilistic automata. We also extend the technique to decide the equivalence of weighted probabilistic automata.

Equivalence of labeled Markov chains

Abstract: We consider the equivalence problem for labeled Markov chains (LMCs), where each state is labeled with an observation. Two LMCs are equivalent if every finite sequence of observations has the same probability of occurrence in the two LMCs. We show that equivalence can be decided in polynomial time, using a reduction to the equivalence problem for probabilistic automata, which is known to be solvable in polynomial time. We provide an alternative algorithm to solve the equivalence problem, which is based on a new definition of bisimulation for probabilistic automata. We also extend the technique to decide the equivalence of weighted probabilistic automata.

Visibly pushdown transducers

Abstract: Visibly pushdown automata have been recently introduced by Alur and Madhusudan as a subclass of pushdown automata. This class enjoys nice properties such as closure under all Boolean operations and the decidability of language inclusion. Along the same line, we introduce here visibly pushdown transducers as a subclass of pushdown transducers. We study properties of those transducers and identify subclasses with useful properties like decidability of type checking as well as preservation of regularity of visibly pushdown languages.

From Many Places to Few: Automatic Abstraction Refinement for Petri Nets

Abstract: Current algorithms for the automatic verification of Petri nets suffer from the explosion caused by the high dimensionality of the state spaces of practical examples. In this paper, we develop an abstract interpretation based analysis that reduces the dimensionality of state spaces that are explored during verification. In our approach, the dimensionality is reduced by trying to gather places that may not be important for the property to establish. If the abstraction that is obtained is too coarse, an automatic refinement is performed and a more precise abstraction is obtained. The refinement is computed by taking into account information about the inconclusive analysis. The process is iterated until the property is proved to be true or false.

ALASKA: antichains for logic, automata and symbolic Kripke structures analysis

Abstract: ALASKA is a verification tool that implements new algorithms based on antichains [5, 7, 6] to efficiently solve the emptiness problem for both alternating finite automata (AFW) and alternating Buchi automata (ABW). Using the well-known translation from LTL to alternating automata, the tool can decide the satisfiability and validity problems for LTL over finite or infinite words. Moreover, ALASKA can solve the model-checking problem for ABW, LTL, AFW and finite-word LTL over symbolic (BDD-encoded) Kripke structures. © 2008 Springer Berlin Heidelberg.

Durations and parametric model-checking in timed automata

Abstract: We consider the problem of model-checking a parametric extension of the logic TCTL over timed automata and establish its decidability. Given a timed automaton, we show that the set of durations of runs starting from a region and ending in another region is definable in Presburger arithmetic (when the time domain is discrete) or in a real arithmetic (when the time domain is dense). Using this logical definition, we show that the parametric model-checking problem for the logic TCTL can be solved algorithmically; the proof of this result is simple. More generally, we are able to effectively characterize the values of the parameters that satisfy the parametric TCTL formula with respect to the given timed automaton.

Visibly Pushdown Transducers

Abstract: Visibly pushdown automata have been recently introduced by Alur and Madhusudan as a subclass of pushdown automata. This class enjoys nice properties such as closure under all Boolean operations and the decidability of language inclusion. Along the same line, we introduce here visibly pushdown transducers as a subclass of pushdown transducers. We study properties of those transducers and identify subclasses with useful properties like decidability of type checking as well as preservation of regularity of visibly pushdown languages.