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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 23 (10 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.
Verifying Progress in Timed Systems
 In ARTS'99
, 1999
"... In this paper we study the issue of progress for distributed timed systems modeled as the parallel composition of timed automata. We clarify the requirements of discrete progress (absence of deadlocks) and time progress (absence of deadlocks and timelocks) and give static sufficient conditions for a ..."
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Cited by 22 (1 self)
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In this paper we study the issue of progress for distributed timed systems modeled as the parallel composition of timed automata. We clarify the requirements of discrete progress (absence of deadlocks) and time progress (absence of deadlocks and timelocks) and give static sufficient conditions for a model of TA to be deadlock and timelockfree. We also present dynamic techniques for deadlock and timelock detection. The techniques are based on forward symbolic reachability and are onthefly, that is, they can return an answer as soon as possible, without necessarily having to construct and store the whole state space.
Tabled Resolution + Constraints: A Recipe for Model Checking RealTime Systems
 In IEEE Real Time Systems Symposium (RTSS
, 1999
"... We present a computational framework based on tabled resolution and constraint processing for verifying realtime systems. We also discuss the implementation of this framework in the context of the XMC/RT verication tool. For systems specied using timed automata, XMC/RT oers backward and forward ..."
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Cited by 21 (5 self)
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We present a computational framework based on tabled resolution and constraint processing for verifying realtime systems. We also discuss the implementation of this framework in the context of the XMC/RT verication tool. For systems specied using timed automata, XMC/RT oers backward and forward reachability analysis, as well as timed modal mucalculus model checking. It can also handle timed innitestate systems, such as those with unbounded message buers, provided the set of reachable states is nite. We illustrate this capability on a realtime version of the leader election protocol. Finally, XMC/RT can function as a model checker for untimed systems. Despite this versatility, preliminary benchmarking experiments indicate that XMC/RT's performance remains competitive with that of other realtime verication tools. 1 Introduction In a recent paper [RRR + 97], we showed that logic programming with tabulation can be used to construct an ecient model checker for untime...
Symbolic model checking for rectangular hybrid systems
 TACAS 2000: Tools and algorithms for the construction and analysis of systems, Lecture Notes in Computer Science, NewYork
, 2000
"... Abstract. An important case of hybrid systems are the rectangular automata. First, rectangular dynamics can naturally and arbitrarily closely approximate more general, nonlinear dynamics. Second, rectangular automata are the most general type of hybrid systems for which model checking in particular ..."
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Cited by 17 (2 self)
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Abstract. An important case of hybrid systems are the rectangular automata. First, rectangular dynamics can naturally and arbitrarily closely approximate more general, nonlinear dynamics. Second, rectangular automata are the most general type of hybrid systems for which model checking in particular, Ltl model checking  is decidable. However, on one hand, the original proofs of decidability did not suggest practical algorithms and, on the other hand, practical symbolic modelchecking procedures such as those implemented in HyTech  were not known to terminate on rectangular automata. We remedy this unsatisfactory situation: we present a symbolic method for Ltl model checking which can be performed by HyTech and is guaranteed to terminate on all rectangular automata. We dosoby proving that our method for symbolic Ltl model checking terminates on an in nitestate transition system if the traceequivalence relation of the system has nite index, which is the case for all rectangular automata. 1
Inference of eventrecording automata using timed decision trees
 Lecture Notes in Computer Science, 4137:435–449, 2006. In Proceedings of the 17th International Conference on Concurrency Theory
, 2006
"... In regular inference, the problem is to infer a regular language, typically represented by a deterministic finite automaton (DFA) from answers to a finite set of membership queries, each of which asks whether the language contains a certain word. There are many algorithms for learning DFAs, the most ..."
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Cited by 12 (3 self)
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In regular inference, the problem is to infer a regular language, typically represented by a deterministic finite automaton (DFA) from answers to a finite set of membership queries, each of which asks whether the language contains a certain word. There are many algorithms for learning DFAs, the most wellknown being the algorithm due to Dana Angluin. However, there are almost no extensions of these algorithms to the setting of timed systems. We present an algorithm for inferring a model of a timed system using Angluin’s setup. One of the most popular model for timed system is timed automata. Since timed automata can freely use an arbitrary number of clocks, we restrict our attention to systems that can be described by eventrecording automata (DERAs). In previous work, we have presented an algorithm for inferring a DERA in the form of a region graph. In this paper, we present a novel inference algorithm for DERAs, which avoids constructing a (usually prohibitively large) region graph. We must then develop techniques for inferring guards on transitions of a DERA. Our construction deviates from previous work on inference of DERAs in that it first constructs a so called timed decision tree from observations of system behavior, which is thereafter folded into an automaton. 1
Timed unfoldings for networks of timed automata
 Research Rep. LSV0609, Lab. Spécification et Vérification, ENS de
, 2006
"... Abstract. Whereas partial order methods have proved their efficiency for the analysis of discreteevent systems, their application to timed systems remains a challenging research topic. Here, we design a verification algorithm for networks of timed automata with invariants. Based on the unfolding te ..."
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Abstract. Whereas partial order methods have proved their efficiency for the analysis of discreteevent systems, their application to timed systems remains a challenging research topic. Here, we design a verification algorithm for networks of timed automata with invariants. Based on the unfolding technique, our method produces a branching process as an acyclic Petri net extended with read arcs. These arcs verify conditions on tokens without consuming them, thus expressing concurrency between conditions checks. They are useful for avoiding the explosion of the size of the unfolding due to clocks which are compared with constants but not reset. Furthermore, we attach zones to events, in addition to markings. We then compute a complete finite prefix of the unfolding. The presence of invariants goes against the concurrency since it entails a global synchronization on time. The use of read arcs and the analysis of the clock constraints appearing in invariants helps increasing the concurrency relation between events. Finally, the finite prefix can be used to decide reachability properties, and transition enabling. 1
Lower and upper bounds in zone based abstractions of timed automata
 IN: PROCEEDINGS OF THE 10TH INTERNATIONAL CONFERENCE ON TOOLS AND ALGORITHMS FOR CONSTRUCTION AND ANALYSIS OF SYSTEMS (TACAS'04). VOLUME 2988 OF LNCS
, 2004
"... Timed automata have an infinite semantics. For verification purposes, one usually uses zone based abstractions w.r.t. the maximal constants to which clocks of the timed automaton are compared. We show that by distinguishing maximal lower and upper bounds, significantly coarser abstractions can be ..."
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Cited by 10 (2 self)
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Timed automata have an infinite semantics. For verification purposes, one usually uses zone based abstractions w.r.t. the maximal constants to which clocks of the timed automaton are compared. We show that by distinguishing maximal lower and upper bounds, significantly coarser abstractions can be obtained. We show soundness and completeness of the new abstractions w.r.t. reachability. We demonstrate how information about lower and upper bounds can be used to optimise the algorithm for bringing a difference bound matrix into normal form. Finally, we experimentally demonstrate that the new techniques dramatically increases the scalability of the realtime model checker Uppaal.
Specification and Analysis of RealTime Systems with PARAGON
, 1999
"... This paper describes a methodology for the speci cation and analysis of distributed realtime systems using the toolset called PARAGON. PARAGON is based on the Communicating Shared Resources paradigm, which allows a realtime system to be modeled as a set of communicating processes that compete for ..."
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Cited by 9 (7 self)
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This paper describes a methodology for the speci cation and analysis of distributed realtime systems using the toolset called PARAGON. PARAGON is based on the Communicating Shared Resources paradigm, which allows a realtime system to be modeled as a set of communicating processes that compete for shared resources. PARAGON supports both visual and textual languages for describing realtime systems. It o ers automatic analysis based on state space exploration as well as userdirected simulation. Our experience with using PARAGON in several case studies resulted in a methodology that includes design patterns and abstraction heuristics, as well as an overall process. This paper brie y overviews the communicating shared resource paradigm and its toolset PARAGON, including the textual and visual speci cation languages. The paper then describes our methodology with special emphasis on heuristics that can be used in PARAGON to reduce the state space. To illustrate the methodology, we use examples from a reallife system case study.
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 8 (6 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.