J. Sifakis

Bio: J. Sifakis is an academic researcher. The author has contributed to research in topics: Formal verification & Formal specification. The author has an hindex of 1, co-authored 1 publications receiving 26 citations.

Priority systems [deadlock-free systems]

Abstract: We present a framework for the incremental construction of deadlock-free systems meeting given safety properties. The framework borrows concepts and basic results from the controller synthesis paradigm by considering a step in the construction process as a controller synthesis problem. We show that priorities are expressive enough to represent restrictions induced by deadlock-free controllers preserving safety properties. We define a correspondence between such restrictions and priorities and provide compositionality results about the preservation of this correspondence by operations on safety properties and priorities. Finally, we provide an example illustrating an application of the results

Validating timed UML models by simulation and verification

Abstract: This paper presents a technique and a tool for model-checking operational (design level) UML models based on a mapping to a model of communicating extended timed automata. The target language of the mapping is the IF format, for which existing model-checking and simulation tools can be used. Our approach takes into consideration most of the structural and behavioural features of UML, including object-oriented aspects. It handles the combination of operations, state machines, inheritance and polymorphism, with a particular semantic profile for communication and concurrency. We adopt a UML profile that includes extensions for expressing timing. The breadth of concepts covered by our mapping is an important point, as many previous approaches for applying formal validation to UML put much stronger limitations on the considered models. For expressing properties about models, a formalism called UML observers is defined in this paper. Observers reuse existing concepts like classes and state machines, and they allow expressing a significant class of linear temporal properties. The approach is implemented in a tool that imports UML models from an XMI repository, thus supporting several editors like Rational Rose, Rhapsody or Argo. The generated IF models may be simulated and verified via an interface that presents feedback in the vocabulary of the original UML model.

A framework for component-based construction

Abstract: We present an overview of results developed mainly at Verimag, by the author and his colleagues, on a framework for component-based construction, characterized by the following: the behavior of atomic components is represented by transition systems; components are built from a set of atomic components by using "glue" operators; for each component, it is possible to separate its behavior from its structure, due to specific properties of glue operators. We show an instance of this framework, which combines two independent classes of glue operators, interaction models and priorities. The combination of interaction models and priorities is expressive enough to encompass heterogeneous interaction and execution. We show that separation between behavior and structure is instrumental for correctness-by-construction. Finally, we discuss new research problems related to a structure-dependent notion of expressiveness.

Distributed Semantics and Implementation for Systems with Interaction and Priority

Abstract: The paper studies a distributed implementation method for the BIP (Behavior, Interaction, Priority) component framework for modeling heterogeneous systems. BIP offers two powerful mechanisms for describing composition of components by combining interactions and priorities. A system model is layered. The lowest layer contains atomic components; the second layer, describes possible interactions between atomic components; the third layer includes priorities between the interactions. The current implementation of BIP is based on global state operational semantics. An Engine directly interprets the operational semantics rules and computes the possible interactions between atomic components from global states. The implementation method is a translation from BIP models into distributed models involving two steps. The first translates BIP models into partial state models where are known only the states of the components which are ready to communicate. The second implements interactions in the partial state model by using message passing primitives. The main results of the paper are conditions for which the three models are observationally equivalent. We show that in general, the translation from global state to partial state models does not preserve observational equivalence. Preservation can be achieved by strengthening the premises of the operational semantics rules by an oracle. This is a predicate depending on the priorities of the BIP model. We show that there are many possible choices for oracles. Maximal parallelism is achieved for dynamic oracles allowing interaction as soon as possible. Nonetheless, these oracles may entail considerable computational overhead. We study performance trade-offs for different types of oracles. Finally, we provide experimental results illustrating the application of the theory on a prototype implementation.

An Approach to Modelling and Verification of Component Based Systems

Abstract: We build on a framework for modelling and investigating component-based systems that strictly separates the description of behavior of components from the way they interact. We discuss various properties of system behavior as liveness, local progress, local and global deadlock, and robustness. We present a criterion that ensures liveness and can be tested in polynomial time.

Model checking bounded prioritized time Petri nets

Abstract: In a companion paper [BPV06], we investigated the expressiveness of Time Petri Nets extended with Priorities and showed that it is very close to that Timed Automata, in terms of weak timed bisimilarity. As a continuation of this work we investigate here the applicability of the available state space abstractions for Bounded Time Petri Nets to Bounded Prioritized Time Petri Nets. We show in particular that a slight extension of the "strong state classes" construction of [BV03] provides a convenient state space abstraction for these nets, preserving markings, states, and LTL formulas. Interestingly, and conversely to Timed Automata, the construction proposed does not require to compute polyhedra differences.