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

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

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

Modeling heterogeneous real-time components in BIP

We present a methodology for modeling heterogeneous real-time components. Components are obtained as the superposition of three layers: behavior, specified as a set of transitions; Interactions between transitions of the behavior; Priorities, used to choose amongst possible interactions. A parameterized binary composition operator is used to compose components layer by layer. We present the BIP language for the description and composition of layered components as well as associated tools for executing and analyzing components on a dedicated platform. The language provides a powerful mechanism for structuring interactions involving rendezvous and broadcast. We show that synchronous and timed systems are particular classes of components. Finally, we provide examples and compare the BIP framework to existing ones for heterogeneous component-based modelin

Scheduler modeling based on the controller synthesis paradigm

The controller synthesis paradigm provides a general framework for scheduling real-time applications. Schedulers can be considered as controllers of the applications; they restrict their behavior so that given scheduling requirements are met. We study a modeling methodology based on the controller synthesis paradigm. The methodology allows to get a correctly scheduled system from timed models of its processes in an incremental manner, by application of composability results which simplify schedulability analysis. It consists in restricting successively the system to be scheduled by application of constraints defined from scheduling requirements. The latter are a conjunction of schedulability requirements that express timing properties of the processes and policy requirements about resource management. The presented methodology allows a unified view of scheduling theory and approaches based on timing analysis of models of real-time applications