A partial order semantics approach to the clock explosion problem of timed automata

Lugiez, Denis; Niebert, Peter; Zennou, Sarah

doi:10.1016/j.tcs.2005.07.023

Cited by 47 publications

(64 citation statements)

References 28 publications

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“…This work which has been done in parallel with the development of the first verification tools for timed automata, uses another terminology and has not proliferated to the timed automaton culture. Two more recent efforts, which are more ambitious with respect to full-fledged partial-order reductions, are those of Zhao [Z02] and of Niebert et al [ZYN03,LNZ05]. Both works use additional clocks in their algorithms and use zones over the extended clock space ("event zones" in the terminology of [ZYN03,LNZ05], "local successors" in the terminology of [Z02]) that represent all configurations reached by interleavings of independent actions.…”

Section: Related Work and Discussionmentioning

confidence: 99%

On Interleaving in Timed Automata

Salah

Bozga

Maler

2006

CONCUR 2006 – Concurrency Theory

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Abstract. We propose a remedy to that part of the state-explosion problem for timed automata which is due to interleaving of actions. We prove the following quite surprising result: the union of all zones reached by different interleavings of the same set of transitions is convex. Consequently we can improve the standard reachability computation for timed automata by merging such zones whenever they are encountered. Since passage of time distributes over union, we can continue the successor computation from the new zone and eliminate completely the explosion due to interleaving.

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Section: Related Work and Discussionmentioning

confidence: 99%

On Interleaving in Timed Automata

Salah

Bozga

Maler

2006

CONCUR 2006 – Concurrency Theory

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“…Extending decidability results to distributed systems has been done only in two particular and limited settings. In the first setting, [13,8] consider clocks that are local to a process. But then, one cannot specify time taken by a communication (message or synchronization).…”

Section: Introductionmentioning

confidence: 99%

Symbolically Bounding the Drift in Time-Constrained MSC Graphs

Akshay

Genest

Hélouët

et al. 2012

Theoretical Aspects of Computing – ICTAC 2012

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Systems involving both time and concurrency are notoriously difficult to analyze. Existing decidability results apply in settings where clocks on different processes cannot be compared or where the set of timed executions is regular. We prove new decidability results for timed concurrent systems, requiring neither restriction. We consider the formalism of time-constrained MSC graphs (TC-MSC graphs for short), introduced in [2]. We study the problem of checking whether the set of timed executions generated by a TC-MSC graph is empty, which is undecidable in general [9].In this paper, we show the decidability of this problem under the restriction that every path of the TC-MSC graph is prohibited from forcing any basic scenario labeling a node to take more than K units of time to complete, for a given K. Further, we prove that this condition can be effectively checked. Our approach consists in encoding the time constraints seen along a path into a bounded system of inequalities. Instead of constructing an interleaved model and using zones of timed automata as in existing approaches, we symbolically manipulate the system of inequalities using the Fourier-Motzkin elimination method. This allows for decision procedures which are both efficient and handle non regular specifications. IntroductionIn a distributed system, several processes interact to implement a collection of global behaviors. Protocol specifications include timing requirements for messages as well as descriptions of how to recover from timeouts. Thus, a protocol designer has to deal with situations where time and concurrency influence each other. One way to describe these interactions is through scenarios, formalized using Message Sequence Charts (MSCs) [11]. The timing information is captured by adding timing constraints between pairs of events, yielding time-constrained MSCs (denoted TC-MSCs). A protocol is then described by allowing choices and repetition of scenarios. To specify these main characteristics of protocols while abstracting away details of implementation, the formal methods community often considers MSC graphs, which are directed graphs whose nodes are labeled by MSCs. MSC graphs have been generalized to time-constrained MSC graphs (TC-MSC graphs) [2], whose nodes are labeled by TC-MSCs and edges have additional timing constraints. In general, such models do not have regular sets of executions. In this paper, we consider decidability issues for TC-MSC graphs.Obtaining decidability in the presence of both time and concurrency is a challenging issue. For instance, even checking whether there exists a timed execution that is consistent with all the constraints of a model is non trivial. This question, called the emptiness problem, is undecidable for TC-MSC graphs in general [9]. However, it is decidable for (sequential) timed automata [3]. Extending decidability results to distributed systems has been done only in two particular and limited settings. In the first setting, [13,8] consider clocks that are local to a process. But then,...

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“…The efficiency of this method depends on two opposite factors: local time semantics generate more states but the independence relation restricts the exploration. In [15] (a generalization of [22]), the independence between transitions in a TA is exploited in a different way: the key observation is that the occurrences of two independent transitions do no need to be ordered and consequently nor do the occurrences of the clock resets. The relative drawback of the method is that, before their exploration, the symbolic states include more variables than the clock variables.…”

Section: Introductionmentioning

confidence: 99%

Symbolic Unfoldings for Networks of Timed Automata

Cassez

Chatain

Jard

2006

Automated Technology for Verification and Analysis

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Abstract. In this paper we give a symbolic concurrent semantics for network of timed automata (NTA) in terms of extended symbolic nets. Extended symbolic nets are standard occurrence nets extended with read arcs and symbolic constraints on places and transitions. We prove that there is a complete finite prefix for any NTA that contains at least the information of the simulation graph of the NTA but keep explicit the notions of concurrency and causality of the network.

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A partial order semantics approach to the clock explosion problem of timed automata

Cited by 47 publications

References 28 publications

On Interleaving in Timed Automata

On Interleaving in Timed Automata

Symbolically Bounding the Drift in Time-Constrained MSC Graphs

Symbolic Unfoldings for Networks of Timed Automata

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