The compositional specification of timed systems-a tutorial

The analysis of reactive systems requires models representing the system, its interaction with the environment, and taking into account features of the underlying execution structure. It is important that such models are timed if analysis concerns performance, action scheduling or in general, dynamic aspects of the behavior. In practice, timed models of systems are obtained by adding timing constraints to untimed descriptions. For instance, given the functional description of a circuit, the corresponding timed model can be obtained by adding timing constraints about propagation delays of the components; to build a timed model of a real-time software, quantitative timing information concerning execution times of the statements and significant changes of the environment must be added. The construction of timed models of reactive systems raises some important questions concerning their composition and in particular, the way some well-understood constructs for untimed systems can be extended to timed systems. We present an overview of existing executable timed formalisms with a global notion of time, by putting emphasis on problems of compositional description. The results on compositionality have been developed in collaboration with Bornot at Verima

A framework for component-based construction

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 expressivenes

Compositional specification of timed systems

We present timed automata and timed Petri nets and argue that timed automata and their associated parallel composition operator are not well adapted for the compositional description of timed Petri nets. Timed automata with deadlines are presented. We present a compositional translation method from 1-safe timed Petri nets to this model. We also present basic ideas for a general compositional specification framewor

Relating time progress and deadlines in hybrid systems

Time progress conditions in hybrid systems are usually specified in terms of invariants, predicates characterizing states where time can continuously progress, or in terms of deadline conditions, predicates characterizing states where time progress immediately stops. These specifications are each other's duals. The aim of this work is the study of relationships between general time progress conditions and these generated by using state predicates. It is shown that using deadline conditions or invariants allows to characterize all practically interesting time progress conditions. The study is performed by using a Galois connection between the corresponding lattices. We provide conditions for the connection to be a homomorphism and apply the results to the compositional description of hybrid system

Priority systems [deadlock-free systems]

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 result

The embedded systems design challenge

We summarize some current trends in embedded systems design and point out some of their characteristics, such as the chasm between analytical and computational models, and the gap between safety-critical and best-effort engineering practices. We call for a coherent scientific foundation for embedded systems design, and we discuss a few key demands on such a foundation: the need for encompassing several manifestations of heterogeneity, and the need for constructivity in design. We believe that the development of a satisfactory embedded systems design science provides a timely challenge and opportunity for reinvigorating computer scienc

The discipline of embedded systems design

The wall between computer science and electrical engineering has kept the potential of embedded systems at bay. It is time to build a new scientific foundation with embedded systems design as the cornerstone, which will ensure a systematic and even-handed integration of the two fields. The embedded systems design problem certainly raises technology questions, but more important, it requires building a new scientific foundation that will systematically and even-handedly integrate computation and physicality from the bottom up. Support for this foundation will require enriching computer science paradigms to encompass models and methods traditionally found in electrical engineering

A methodology for the construction of scheduled systems

We study a methodology for constructing scheduled systems by restricting successively the behavior of the processes to be scheduled. Restriction is used to guarantee the satisfaction of two types of constraints: schedulability constraints characterizing timing properties of the processes, and constraints characterizing particular scheduling algorithms including process priorities, non-idling, and preemption. The methodology is based on a controller synthesis paradigm. The main results deal with the characterization of scheduling policies as safety constraints and the simplification of the synthesis process by applying a composability principl