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15
Automatic verification of realtime systems with discrete probability distributions
 Theoretical Computer Science
, 1999
"... Abstract. We consider the timed automata model of [3], which allows the analysis of realtime systems expressed in terms of quantitative timing constraints. Traditional approaches to realtime system description express the model purely in terms of nondeterminism; however, we may wish to express the ..."
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Cited by 80 (29 self)
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Abstract. We consider the timed automata model of [3], which allows the analysis of realtime systems expressed in terms of quantitative timing constraints. Traditional approaches to realtime system description express the model purely in terms of nondeterminism; however, we may wish to express the likelihood of the system making certain transitions. In this paper, we present a model for realtime systems augmented with discrete probability distributions. Furthermore, using the algorithm of [5] with fairness, we develop a model checking method for such models against temporal logic properties which can refer both to timing properties and probabilities, such as, “with probability 0.6 or greater, the clock x remains below 5 until clock y exceeds 2”. 1
Checking Reachability Properties for Timed Automata via SAT
 Fundamenta Informaticae
, 2002
"... The paper deals with the problem of checking reachability for timed automata. The main idea consists in combining the wellknow forward reachability algorithm and the Bounded Model Checking (BMC) method. In order to check reachability of a state satisfying some desired property, rst the transition r ..."
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Cited by 17 (8 self)
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The paper deals with the problem of checking reachability for timed automata. The main idea consists in combining the wellknow forward reachability algorithm and the Bounded Model Checking (BMC) method. In order to check reachability of a state satisfying some desired property, rst the transition relation of a timed automaton is unfolded iteratively to the depth k 2 N and encoded as a propositional formula. Next, the desired property is translated to a propositional formula and the satis ability of the conjunction of the two above de ned formulas is checked. The unfolding of the transition relation can be terminated when either a state satisfying the property has been found or all the states of the timed automaton have been searched. The eciency of the method is strongly supported by the experimental results.
Modeling RealTime Systems  Challenges and Work Directions
 In Proceedings of the 1st International Workshop on Embedded Software (EMSOFT), Lecture Notes in Computer Science
, 2001
"... Introduction 1.1 Advanced RealTime Systems The evolution of information sciences and technologies is characterized by the extensive integration of embedded components in systems used in various application areas, from telecommunications to automotive, manufacturing, medical applications, ecommer ..."
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Cited by 11 (0 self)
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Introduction 1.1 Advanced RealTime Systems The evolution of information sciences and technologies is characterized by the extensive integration of embedded components in systems used in various application areas, from telecommunications to automotive, manufacturing, medical applications, ecommerce etc. In most cases, embedded components are realtime systems that continuously interact with other systems and the physical world. Integration and continuous interaction of software and hardware components makes the assurance of global quality a major issue in system design. The failure of a component may have catastrophic consequences on systems performance, security, safety, availability etc. Building embedded realtime systems of guaranteed quality, in a costeective manner, raises challenging scienti c and technological problems. Existing theory, techniques and technology are of little help as they fail to provide a global framework relating various design parameters to system dyn
Presburger Liveness Verification of Discrete Timed Automata
, 2003
"... Using an automatatheoretic approach, we investigate the decidability of liveness properties (called Presburger liveness properties) for timed automata when Presburger formulas on configurations are allowed. While the general problem of checking a temporal logic such as TPTL augmented with Presburge ..."
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Cited by 8 (4 self)
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Using an automatatheoretic approach, we investigate the decidability of liveness properties (called Presburger liveness properties) for timed automata when Presburger formulas on configurations are allowed. While the general problem of checking a temporal logic such as TPTL augmented with Presburger clock constraints is undecidable, we show that there are various classes of Presburger liveness properties which are decidable for discrete timed automata. For instance, it is decidable, given a discrete timed automaton A and a Presburger property P , whether there exists an !path of A where P holds infinitely often. We also show that other classes of Presburger liveness properties are indeed undecidable for discrete timed automata, e.g., whether P holds infinitely often for each !path of A . These results might give insights into the corresponding problems for timed automata over dense domains, and help in the definition of a fragment of linear temporal logic, augmented with Presburger conditions on configurations, which is decidable for model checking timed automata.
Checking Timed Büchi Automata Emptiness on Simulation Graphs
, 2006
"... This paper completes the work of [5,13] on checking language emptiness of timed Büchi automata efficiently. In [5,13] we showed how to check emptiness on the regionclosed simulation graph. However, the latter is not used in practice, since its nodes are nonconvex, thus, not easily representable. U ..."
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Cited by 5 (1 self)
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This paper completes the work of [5,13] on checking language emptiness of timed Büchi automata efficiently. In [5,13] we showed how to check emptiness on the regionclosed simulation graph. However, the latter is not used in practice, since its nodes are nonconvex, thus, not easily representable. Using recent results of Bouyer [6] on simulationgraph overapproximations that preserve convexity, we show that the main result of [5,13] carries over to the zoneclosed simulation graph. The nodes of the latter are convex and can be efficiently represented. The zoneclosed simulation graph is used in the tools Kronos and Uppaal for checking reachability. Our result shows that these tools can be also used to check emptiness of timed Büchi automata with small modifications.
Model Checking for Probabilistic Timed Systems
 In Validation of Stochastic Systems – A Guide to Current Research, volume 2925 of LNCS
, 2004
"... Application areas such as multimedia equipment, communication protocols and networks often feature systems which exhibit both probabilistic and timed behaviour. In this paper, we consider analysis of such probabilistic timed systems using the technique of model checking, in which it is verified ..."
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Cited by 5 (0 self)
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Application areas such as multimedia equipment, communication protocols and networks often feature systems which exhibit both probabilistic and timed behaviour. In this paper, we consider analysis of such probabilistic timed systems using the technique of model checking, in which it is verified automatically whether a system satisfies a certain desired property. In order to describe formally probabilistic timed systems, we consider probabilistic extensions of timed automata, such as realtime probabilistic processes, probabilistic timed automata and continuous probabilistic timed automata, the underlying semantics of each of which is an infinitestate structure. For each formalism, we consider how the wellknown region equivalence relation can be used to reduce the infinite statespace model into a finitestate system, which can then be used for model checking.
Towards Bounded Model Checking for the Universal Fragment of TCTL
, 2002
"... Bounded Model Checking (BMC) based on SAT methods consists in searching for a counterexample of a particular length and to generate a propositional formula that is satis able i such a counterexample exists. Our paper shows how the concept of bounded model checking can be extended to deal with T ..."
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Cited by 4 (3 self)
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Bounded Model Checking (BMC) based on SAT methods consists in searching for a counterexample of a particular length and to generate a propositional formula that is satis able i such a counterexample exists. Our paper shows how the concept of bounded model checking can be extended to deal with TACTL (the universal fragment of TCTL) properties of Timed Automata.
Simplifying Fixpoint Computations in Verification of RealTime Systems
, 2002
"... Symbolic verification of realtime systems consists of computing the least fixpoint of a functional which given a set of states returns the states that are reachable from (in forward reachability), or that can reach (in backward reachability). This paper presents two techniques for simplifying the f ..."
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Cited by 4 (0 self)
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Symbolic verification of realtime systems consists of computing the least fixpoint of a functional which given a set of states returns the states that are reachable from (in forward reachability), or that can reach (in backward reachability). This paper presents two techniques for simplifying the fixpoint computation: First, I demonstrate that in backwards reachability, clock resets and discrete state changes can be performed as substitutions instead of existential quantifications over reals and Booleans, respectively. Second, I introduce a localtime model for realtime systems which allows clocks to advance asynchronously, thus resulting in an overapproximation of the least fixpoint, but which in some cases is sufficient for verifying a temporal property.
Model checking restricted sets of timed paths
 Theoretical Computer Science
, 2005
"... Abstract. In this paper, we study the complexity of modelchecking formulas of three important realtime logics (MTL, MITL, and TCTL) over restricted sets of timed paths. The classes of restricted sets of timed paths that we consider are (i) a single finite (or ultimately periodic) timed path, (ii) ..."
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Cited by 3 (1 self)
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Abstract. In this paper, we study the complexity of modelchecking formulas of three important realtime logics (MTL, MITL, and TCTL) over restricted sets of timed paths. The classes of restricted sets of timed paths that we consider are (i) a single finite (or ultimately periodic) timed path, (ii) a infinite set of finite (or infinite) timed paths defined by a finite (or ultimately periodic) path in a region graph, (iii) a infinite set of finite (or infinite) timed paths defined by a finite (or ultimately periodic) path in a zone graph.
Reachability Analysis for Timed Automata Based on Partitioning
, 2003
"... Model checking is an approach commonly applied for automated veri cation of reachability properties. Given a system S and a property p, reachability model checking consists in an exploration of the state space of S, checking whether there exists a state where p holds. Since concrete state spaces (m ..."
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Cited by 2 (2 self)
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Model checking is an approach commonly applied for automated veri cation of reachability properties. Given a system S and a property p, reachability model checking consists in an exploration of the state space of S, checking whether there exists a state where p holds. Since concrete state spaces (models) of timed systems are usually in nite, they cannot be directly applied to model checking. One of the solution to this problem is to exploit nite abstract models, preseving the properties of interest. The paper presents a new method of buildng abstract models for Timed Automata, based on a partitioning algorithm. Our pseudobisimulating models are often smaller than forwardreachability graphs, commonly used in reachability analysis. The method enables veri cation onthey, i.e., generating of the model can be stopped as soon as a state satisfying p is found.