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Shrinking timed automata
 In FSTTCS’11, LIPIcs 13, p. 375–386. LeibnizZentrum für Informatik
, 2011
"... We define and study a new approach to the implementability of timed automata, where the semantics is perturbed by imprecisions and finite frequency of the hardware. In order to circumvent these effects, we introduce parametric shrinking of clock constraints, which corresponds to tightening these. We ..."
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Cited by 32 (12 self)
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We define and study a new approach to the implementability of timed automata, where the semantics is perturbed by imprecisions and finite frequency of the hardware. In order to circumvent these effects, we introduce parametric shrinking of clock constraints, which corresponds to tightening these. We propose symbolic procedures to decide the existence of (and then compute) parameters under which the shrunk version of a given timed automaton is nonblocking and can timeabstract simulate the exact semantics. We then define an implementation semantics for timed automata with a digital clock and positive reaction times, and show that for shrinkable timed automata, nonblockingness and timeabstract simulation are preserved in implementation.
Robustness and Implementability of Timed Automata
 In Proc. Joint Conf. Formal Modelling and Analysis of Timed Systems and Formal Techniques in RealTime and Fault Tolerant System (FORMATS+FTRTFT’04), volume 3253 of LNCS
, 2004
"... In a former paper, we de ned a new semantics for timed automata, the Almost ASAP semantics, which is parameterized by to cope with the reaction delay of the controller. We showed that this semantics is implementable provided there exists a strictly positive value for the parameter for which t ..."
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Cited by 20 (10 self)
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In a former paper, we de ned a new semantics for timed automata, the Almost ASAP semantics, which is parameterized by to cope with the reaction delay of the controller. We showed that this semantics is implementable provided there exists a strictly positive value for the parameter for which the strategy is correct. In this paper, we de ne the implementability problem to be the question of existence of such a . We show that this question is closely related to a notion of robustness for timed automata de ned in [Pur98] and prove that the implementability problem is decidable.
Robust Safety of Timed Automata
 FORMAL METHODS IN SYSTEM DESIGN
"... 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 wo ..."
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Cited by 11 (7 self)
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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 ∆> 0 and clocks can drift by ε> 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 ∆ and ε such that the timed automaton never enters the bad states under the relaxed semantics.
Robust modelchecking of lineartime properties in timed automata
 Proceedings of the 7th Latin American Symposium on Theoretical Informatics (LATIN’06), volume 3887 of Lecture
"... Abstract. Formal verification of timed systems is well understood, but their implementation is still challenging. Raskin et al. have recently brought out a model of parameterized timed automata in which the transitions might be slightly delayed or expedited. This model is used to prove that a timed ..."
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Cited by 10 (5 self)
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Abstract. Formal verification of timed systems is well understood, but their implementation is still challenging. Raskin et al. have recently brought out a model of parameterized timed automata in which the transitions might be slightly delayed or expedited. This model is used to prove that a timed system is implementable with respect to a safety property, by proving that the parameterized model robustly satisfies the safety property. We extend here the notion of implementability to the broader class of lineartime properties, and provide PSPACE algorithms for the robust modelchecking of Büchilike and LTL properties. We also show how those algorithms can be adapted in order to verify boundedresponsetime properties.
Robust analysis of timed automata via channel machines
, 2007
"... Abstract. Whereas formal verification of timed systems has become a very active field of research, the idealised mathematical semantics of timed automata cannot be faithfully implemented. Several works have thus focused on a modified semantics of timed automata which ensures implementability, and ro ..."
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Cited by 10 (5 self)
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Abstract. Whereas formal verification of timed systems has become a very active field of research, the idealised mathematical semantics of timed automata cannot be faithfully implemented. Several works have thus focused on a modified semantics of timed automata which ensures implementability, and robust modelchecking algorithms for safety, and later LTL properties have been designed. Recently, a new approach has been proposed, which reduces (standard) modelchecking of timed automata to other verification problems on channel machines. Thanks to a new encoding of the modified semantics as a network of timed systems, we propose an original combination of both approaches, and prove that robust modelchecking for coFlatMTL, a large fragment of MTL, is EXPSPACEComplete. 1
ModelBased Implementation of RealTime Applications
"... Correct and efficient implementation of general realtime applications remains by far an open problem. A key issue is meeting timing constraints whose satisfaction depends on features of the execution platform, in particular its speed. Existing rigorous implementation techniques are applicable to sp ..."
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Cited by 9 (1 self)
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Correct and efficient implementation of general realtime applications remains by far an open problem. A key issue is meeting timing constraints whose satisfaction depends on features of the execution platform, in particular its speed. Existing rigorous implementation techniques are applicable to specific classes of systems e.g. with periodic tasks, time deterministic systems. We present a general modelbased implementation method for realtime systems based on the use of two models. • An abstract model representing the behavior of realtime software as a timed automaton. The latter describes userdefined platformindependent timing constraints. Its transitions are timeless and correspond to the execution of statements of the realtime software.
Robustness in realtime systems
 In SIES’11
"... We review several aspects of robustness of realtime systems, and present recent results on the robust verification of timed automata. 1 ..."
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Cited by 6 (3 self)
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We review several aspects of robustness of realtime systems, and present recent results on the robust verification of timed automata. 1
Sampled Semantics of Timed Automata
"... Sampled semantics of timed automata is a finite approximation of their dense time behavior. While the former is closer to the actual character of the latter makes it appealing for system modeling and verification. We study one aspect of the relation between these two semantics, namely checking wheth ..."
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Cited by 6 (0 self)
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Sampled semantics of timed automata is a finite approximation of their dense time behavior. While the former is closer to the actual character of the latter makes it appealing for system modeling and verification. We study one aspect of the relation between these two semantics, namely checking whether the system exhibits some qualitative (untimed) behaviors in the dense time which cannot be reproduced by any implementation with a fixed sampling rate. More formally, the sampling problem is to decide whether there is a sampling rate such that all qualitative behaviors (the untimed language) accepted by a given timed automaton in dense time semantics can be also accepted in sampled semantics. We show that this problem is decidable.
Symbolic robustness analysis of timed automata
 In Proc. 4th Intl Conf. Formal Modeling and Analysis of Timed Systems (FORMATS’06), LNCS 4202
, 2006
"... Abstract. We propose a symbolic algorithm for the analysis of the robustness of timed automata, that is the correctness of the model in presence of small drifts on the clocks or imprecision in testing guards. This problem is known to be decidable with an algorithm based on detecting strongly connect ..."
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Cited by 5 (0 self)
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Abstract. We propose a symbolic algorithm for the analysis of the robustness of timed automata, that is the correctness of the model in presence of small drifts on the clocks or imprecision in testing guards. This problem is known to be decidable with an algorithm based on detecting strongly connected components on the region graph, which, for complexity reasons, is not effective in practice. Our symbolic algorithm is based on the standard algorithm for symbolic reachability analysis using zones to represent symbolic states and can then be easily integrated within tools for the verification of timed automata models. It relies on the computation of the stable zone of each cycle in a timed automaton. The stable zone is the largest set of states that can reach and be reached from itself through the cycle. To compute the robust reachable set, each stable zone that intersects the set of explored states has to be added to the set of states to be explored. 1
Untimed language preservation in timed systems
 In Proc. of MFCS’11, LNCS
, 2011
"... Abstract. Timed automata are a model that is extensively used in formal verification of realtime systems. However, their mathematical semantics is an idealization which assumes perfectly precise clocks, but does not correspond to real hardware. In fact, it is known that imprecisions, however small ..."
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Cited by 4 (3 self)
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Abstract. Timed automata are a model that is extensively used in formal verification of realtime systems. However, their mathematical semantics is an idealization which assumes perfectly precise clocks, but does not correspond to real hardware. In fact, it is known that imprecisions, however small they may be, may yield extra behaviours. Several works concentrated on a relaxation of the semantics of timed automata to model the imprecisions of the clocks. Algorithms were given, first for safety, then for richer lineartime properties, to decide the robustness of timed systems, that is, the existence of a bound on the imprecisions under which the system satisfies a given property. In this work, we study a stronger notion of robustness: we show how to decide whether the untimed language of a timed automaton is preserved under small enough imprecisions, and provide a bound on the imprecision parameter. 1