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28
From Timed to Hybrid Systems
"... We propose a framework for the formal speci cation and veri cation of timed and hybrid systems. For timed systems we propose a speci cation language that refers to time only through age functions which measure the length of the most recent timeinterval in which agiven formula has been continuously t ..."
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Cited by 146 (16 self)
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We propose a framework for the formal speci cation and veri cation of timed and hybrid systems. For timed systems we propose a speci cation language that refers to time only through age functions which measure the length of the most recent timeinterval in which agiven formula has been continuously true. We then consider hybrid systems, which are systems consisting of a nontrivial mixture of discrete and continuous components, such as a digital controller that controls acontinuous environment. The proposed framework extends the temporal logic approach which has proven useful for the formal analysis of discrete systems such as reactive programs. The new framework consists of a semantic model for hybrid time, the notion of phase transition systems, which extends the formalism of discrete transition systems, an extended version of Statecharts for the speci cation of hybrid behaviors, and an extended version of temporal logic that enables reasoning about continuous change.
An overview and synthesis on timed process algebras
, 1991
"... We present anoverview and synthesis of existing results about process algebras for the speci cation and analysis of timed systems. The motivation is double: present anoverview of some relevant and representative approaches and suggest a unifying framework for them. time, we propose a general model f ..."
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Cited by 140 (4 self)
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We present anoverview and synthesis of existing results about process algebras for the speci cation and analysis of timed systems. The motivation is double: present anoverview of some relevant and representative approaches and suggest a unifying framework for them. time, we propose a general model for them: transition systems whose labels are either elements ofavocabulary of actions or elements of a time domain. Many properties of this model are studied concerning their impact on description capabilities and on realisability issues. An overview of the language features of the process algebras considered is presented, by focusing on constructs used to express time constraints. The presentation is organised as an exercise of building a timed process algebra from a standard process algebra for untimed systems. The overview is completed by a discussion about description capabilities according to semantic and pragmatic criteria. 1
What Good Are Digital Clocks?
, 1992
"... . Realtime systems operate in "real," continuous time and state changes may occur at any realnumbered time point. Yet many verification methods are based on the assumption that states are observed at integer time points only. What can we conclude if a realtime system has been shown "correct" ..."
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Cited by 109 (14 self)
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. Realtime systems operate in "real," continuous time and state changes may occur at any realnumbered time point. Yet many verification methods are based on the assumption that states are observed at integer time points only. What can we conclude if a realtime system has been shown "correct" for integral observations? Integer time verification techniques suffice if the problem of whether all realnumbered behaviors of a system satisfy a property can be reduced to the question of whether the integral observations satisfy a (possibly modified) property. We show that this reduction is possible for a large and important class of systems and properties: the class of systems includes all systems that can be modeled as timed transition systems; the class of properties includes timebounded invariance and timebounded response. 1 Introduction Over the past few years, we have seen a proliferation of formal methodologies for software and hardware design that emphasize the treatm...
The Algebra of Timed Processes ATP: Theory and Application
 INFORMATION AND COMPUTATION
, 1994
"... We study a process algebra ATP for the description and analysis of systems of timed processes. An important feature of the algebra is that its vocabulary of actions contains a distinguished element . An occurrence of is a time event representing progress of time. The algebra has, apart from standar ..."
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Cited by 105 (4 self)
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We study a process algebra ATP for the description and analysis of systems of timed processes. An important feature of the algebra is that its vocabulary of actions contains a distinguished element . An occurrence of is a time event representing progress of time. The algebra has, apart from standard operators of process algebras like CCS or ACP, a primitive binary unitdelay operator. For two arguments, processes P and Q, this operator gives a process which behaves as P if started before the occurrence of a time action and as Q otherwise. From this operator we define dunit delay operators that can model delay constructs of languages, like timeouts or watchdogs. The use of such operators is illustrated by examples. ATP is provided with a complete axiomatisation with respect to strong bisimulation semantics. It is shown that the algebras obtained by adding the various dunit delay operators to ATP are conservative extensions of it.
Operational and Compositional Semantics of Synchronous Automaton Compositions
, 1992
"... : The state/transition paradigm has been used extensively for the description of eventdriven, parallel systems. However, the lack for hierarchic structure in such descriptions usually prevents us from using this paradigm in a real programming language. We propose the Argos language for reactive ..."
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Cited by 90 (14 self)
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: The state/transition paradigm has been used extensively for the description of eventdriven, parallel systems. However, the lack for hierarchic structure in such descriptions usually prevents us from using this paradigm in a real programming language. We propose the Argos language for reactive systems. The basic components of a program are input/outputlabeled transition systems verifying reactivity (a property similar to inputenabling in IOautomata) . The composition operations (parallel composition and refinement, providing hierarchy) are based upon the synchronous broadcast mechanism of Esterel. We define the language formally in an algebraic framework, and give an operational semantics. The main result is the compositionality of the semantics; we prove that the bisimulation of models induces an equivalence which is a congruence for the operators we propose. An interesting point is the way we introduce hierarchy in a compositional way. 1 1 Introduction The problem ...
From ATP to Timed Graphs and Hybrid Systems
, 1993
"... The paper presents results of ongoing work aiming at the unification of some behavioral description formalisms for timed systems. We propose for the algebra of timed processes ATP a very general semantics in terms of a time domain. It is then shown how ATP can be translated into a variant of timed g ..."
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Cited by 80 (9 self)
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The paper presents results of ongoing work aiming at the unification of some behavioral description formalisms for timed systems. We propose for the algebra of timed processes ATP a very general semantics in terms of a time domain. It is then shown how ATP can be translated into a variant of timed graphs. This result allows the application of existing modelchecking techniques to ATP. Finally, we propose a notion of hybrid systems as a generalization of timed graphs. Such systems can evolve, either by executing a discrete transition, or by performing some "continuous " transformation. The formalisms studied admit the same class of models: time deterministic and time continuous, possibly infinitely branching transition systems labeled by actions or durations.
Compiling RealTime Specifications into Extended Automata
 IEEE Transactions on Software Engineering
, 1992
"... We propose a method for the implementation and analysis of realtime systems, based on the compilation of specifications into extended automata. Such a method has been already adopted for the so called "synchronous" realtime programming languages. ..."
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Cited by 75 (8 self)
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We propose a method for the implementation and analysis of realtime systems, based on the compilation of specifications into extended automata. Such a method has been already adopted for the so called "synchronous" realtime programming languages.
An Efficiency Preorder for Processes
"... A simple efficiency preorder for CCS processes is introduced, in which p ! q means that q is at least as fast as p, or more generally, p uses at least as much resources as q. It is shown to be preserved by all CCS contexts except summation and it is used to analyse a nontrivial example: differe ..."
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Cited by 69 (10 self)
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A simple efficiency preorder for CCS processes is introduced, in which p ! q means that q is at least as fast as p, or more generally, p uses at least as much resources as q. It is shown to be preserved by all CCS contexts except summation and it is used to analyse a nontrivial example: different implementations of a bounded buffer. Finally a sound and complete proof system for finite processes is given. This paper appeared earlier in [1] and [2]. This version of the paper has been revised, corrected and extended to include more operators, more examples and some additional remarks and observations by the first author. Hence all errors are entirely his responsiblity. Most of this work was done while the first author was at the University of Sussex and supported by SERC grant GR/D 97368 of the Science and Engineering Research Council of Great Britain. y The second author would like to acknowledge the support of ESPIRIT II. 1 Introduction A large number of behavioural equivale...
Forward and backward simulations for timingbased systems
 In de Bakker et al
, 1991
"... A general automaton model for timingbased systems is presented and is used as the context for developing a variety of simulation proof techniques for such systems. As a first step, a comprehensive overview of simulation techniques for simple untimed automata is given. In particular, soundness and ..."
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Cited by 63 (16 self)
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A general automaton model for timingbased systems is presented and is used as the context for developing a variety of simulation proof techniques for such systems. As a first step, a comprehensive overview of simulation techniques for simple untimed automata is given. In particular, soundness and completeness results for (1) refinements, (2) forward and backward simulations, (3) forwardbackward and backwardforward simulations, and (4) history and prophecy relations are given. History and prophecy relations are new and are abstractions of the history variables of Owicki and Gries and the prophecy variables of Abadi and Lamport, respectively. As a subsequent step, it is shown how most of the results for untimed automata can be carried over to the setting of timed automata. In fact, many of the results for the timed case are obtained as consequences of the analogous results for the untimed case.
Automatic Verification of RealTime Communicating Systems by ConstraintSolving
 In Proc. of the 7th International Conference on Formal Description Techniques
, 1994
"... this paper, an algebra of timed processes with realvalued clocks is presented, which serves as a formal description language for realtime communicating systems. We show that requirements such as "a process will never reach an undesired state" can be verified by solving a simple class of constrai ..."
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Cited by 43 (15 self)
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this paper, an algebra of timed processes with realvalued clocks is presented, which serves as a formal description language for realtime communicating systems. We show that requirements such as "a process will never reach an undesired state" can be verified by solving a simple class of constraint systems on the clockvariables. A complete method for reachability analysis associated with the language is developed, and implemented as an automatic verification tool based on constraintsolving techniques. Finally as examples, we study and verify the safetyproperties of Fischer's mutual exclusion protocol and a railway crossing controller.