6th International Workshop on Discrete Event Systems (WODES'02)

Departamento de Informática e Ingeniería de Sistemas - Universidad de Zaragoza

Zaragoza, Spain, 2-4 October, 2002

Preliminary Programme

Invited talks

Workshop Programme

From Discrete Event to Hybrid Systems
Christos G. Cassandras

Hybrid systems have emerged as a result of combining conventional time-driven dynamics with event-driven dynamics. This provides an opportunity for frameworks and methodologies developed for discrete event systems to enlarge their scope, driven by applications that range from manufacturing to command-control systems. The goal of this presentation is to explore this transition from the point of view of discrete event system theory. At least some classes of hybrid systems may be viewed as consisting of a lower-level component that corresponds to time-driven physical processes, which a higher-level component with event-driven dynamics is called upon to coordinate by switching between different process operating modes. We will concentrate on the formulation of optimization problems that arise in this “hybrid” setting, where the control variables affect both higher and lower level components, and will invoke optimal control methods to solve such problems. We will also discuss a natural evolution of Perturbation Analysis (PA) techniques for discrete event systems into similar methodologies for a class of hybrid systems known as Stochastic Fluid Models (SFM) that find wide applicability in the control of communication networks.

Model checking embedded system designs
Ed Brinksma

Model checking has established itself as a successful tool supported technique for the verification and debugging of various hardware and software systems. It is also being applied with success to the analysis of the control software in embedded systems. In our presentation we will explain the use of model checking for such systems based on examples, highlighting requirements, weak and strong points of the approach. We address the problem of obtaining good models,which is less straightforward than for ordinary software systems, as they must incorporate the relevant interaction with physical environments. Finally, we discuss new developments based on so-called cost-driven model checking, which can be to find (more) optimal control schedules for certain classes of embedded systems.

Recent Advances in Discrete Analysis and Control of Hybrid Systems
Bruce H. Krogh

A standard approach to the formal analysis of hybrid systems (that is, systems with both continuous and discrete state variables) is to first construct purely discrete-state models, usually by building transition systems based on finite partitions of the continuous state space. Analysis and synthesis techniques for discrete-state systems are then applied to the discrete model to verify properties of the hybrid system and to synthesis supervisory controllers. This approach leads to exact solutions when the discrete-state model is a bisimulation of the hybrid system, but it is well known that bisimulations are guaranteed to exist for only trivial classes of hybrid systems. Consequently, developing techniques for constructing and using conservative discrete-state models of hybrid systems has been a principal theme in hybrid systems literature. In this paper, we review the theory for discrete analysis and control of hybrid systems and assess the progress thus far in creating computational tools based on this theory. The paper concludes with a discussion of several directions for research, with an emphasis on the prospects for developing tools that can deal with problems arising in industrial applications.