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Bliudze S.,CEA Saclay Nuclear Research Center | Sifakis J.,Center Equation
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2011

We study glue operators used in component-based frameworks to obtain systems as the composition of atomic components described as labeled transition systems (LTS). Glue operators map tuples of LTS into LTS. They restrict the behavior of their arguments by performing memoryless coordination. In a previous paper, we have proposed a simple format for SOS rules that captures, in particular, glue operators from known frameworks such as CCS, SCCS, CSP, and BIP. This paper studies a new way for characterizing glue operators: as boolean glue constraints between interactions (sets of ports) and the state of the coordinated components. We provide an SOS format for glue, which allows a natural correspondence between glue operators and glue constraints. This correspondence is used for automated synthesis of glue operators implementing given glue constraints. By focusing on the properties that do not bear computation, we reduce a very hard (and, in general, undecidable) problem of synthesizing controllers to a tractable one. The examples in the paper show that such properties are natural and can be expressed as glue constraints in a straightforward manner. Finally, we compare expressiveness of the proposed formalisms with the glue used in the BIP framework and discuss possible applications. © 2011 Springer-Verlag. Source


Cotton S.,Center Equation
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2010

SMT solvers have traditionally been based on the DPLL(T) algorithm, where the driving force behind the procedure is a DPLL search over truth valuations. This traditional framework allows for a degree of modularity in the treatment of theory solvers. Over time, theory solvers have become more and more closely integrated into the DPLL process, and consequently less and less modular. In this paper, we present a DPLL-like algorithm for SMT solving in which the search takes place over the natural domain of the variables in the problem. As a case study, we analyze its application to continuous domain linear arithmetic, present implementation techniques and some experimentation with difference logic. Results indicate the method can sometimes outperform leading SMT solvers but that the method is not yet robust. © 2010 Springer-Verlag Berlin Heidelberg. Source


Abdellatif T.,Center Equation | Combaz J.,French National Center for Scientific Research | Sifakis J.,French National Center for Scientific Research
Embedded Systems Week 2010 - Proceedings of the 10th ACM International Conference on Compilers, Architecture and Synthesis for Embedded Systems, EMSOFT'10 | Year: 2010

Correct and efficient implementation of general real-time 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 model-based implementation method for real-time systems based on the use of two models. • An abstract model representing the behavior of real-time software as a timed automaton. The latter describes user-defined platform-independent timing constraints. Its transitions are timeless and correspond to the execution of statements of the real-time software. • A physical model representing the behavior of the real-time software running on a given platform. It is obtained by assigning execution times to the transitions of the abstract model. A necessary condition for implementability is time-safety, that is, any (timed) execution sequence of the physical model is also an execution sequence of the abstract model. Time-safety simply means that the platform is fast enough to meet the timing requirements. As execution times of actions are not known exactly, time-safety is checked for worst-case execution times of actions by making an assumption of time-robustness: time-safety is preserved when speed of the execution platform increases. We show that as a rule, physical models are not time-robust and show that time-determinism is a sufficient condition for time-robustness. For given real-time software and execution platform corresponding to a time-robust model, we define an Execution Engine that coordinates the execution of the application software so as to meet its timing constraints. Furthermore, in case of non-robustness, the Execution Engine can detect violations of time-safety and stop execution. Source


Dang T.,French National Center for Scientific Research | Testylier R.,Center Equation
HSCC'11 - Proceedings of the 2011 ACM/SIGBED Hybrid Systems: Computation and Control | Year: 2011

This paper is concerned with the reachability computation for non-linear systems using hybridization. The main idea of hybridization is to approximate a non-linear vector field by a piecewise-affine one. The piecewise-affine vector field is defined by building around the set of current states of the system a simplicial domain and using linear interpolation over its vertices. To achieve a good time-efficiency and accuracy of the reachability computation on the approximate system, it is important to find a simplicial domain which, on one hand, is as large as possible and, on the other hand, guarantees a small interpolation error. In our previous work [8], we proposed a method for constructing hybridization domains based on the curvature of the dynamics and showed how the method can be applied to quadratic systems. In this paper we pursue this work further and present two main results. First, we prove an optimality property of the domain construction method for a class of quadratic systems. Second, we propose an algorithm of curvature estimation for more general non-linear systems with non-constant Hessian matrices. This estimation can then be used to determine efficient hybridization domains. We also describe some experimental results to illustrate the main ideas of the algorithm as well as its performance. Copyright 2011 ACM. Source


Sifakis J.,Center Equation
Formal Methods in System Design | Year: 2010

The Algebra of Connectors AC(P ) is used to model structured interactions in the BIP component framework. Its terms are connectors, relations describing synchronization constraints between the ports of component-based systems. Connectors are structured combinations of two basic synchronization protocols between ports: rendezvous and broadcast. In a previous paper, we have studied interaction semantics for AC(P ) which defines the meaning of connectors as sets of interactions. This semantics reduces broadcasts into the set of their possible interactions and thus blurs the distinction between rendezvous and broadcast. It leads to exponentially complex models that cannot be a basis for efficient implementation. Furthermore, the induced semantic equivalence is not a congruence. For a subset of AC(P ), we propose a new causal semantics that does not reduce broadcast into a set of rendezvous and explicitly models the causal dependency relation between ports. The Algebra of Causal Interaction Trees T (P ) formalizes this subset. It is the set of the terms generated from interactions on the set of ports P, by using two operators: a causality operator and a parallel composition operator. Terms are sets of trees where the successor relation represents causal dependency between interactions: an interaction can participate in a global interaction only if its father participates too. We show that causal semantics is consistent with interaction semantics; the semantic equivalence on T (P ) is a congruence. Furthermore, it defines an isomorphism between T (P ) and a subset of AC(P ). Finally, we define for causal interaction trees a boolean representation in terms of causal rules. This representation is used for their manipulation and simplification as well as for synthesizing connectors. © Springer Science+Business Media, LLC 2009. Source

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