Introduction

Reactive systems are computer systems that continuously react to their environment at a speed determined by this environment. This class of systems has been introduced [HP85, Ber89] in order to distinguish these systems, on the one hand, from transformational systems — i.e., classical systems, whose inputs are available at the beginning of the execution and which deliver their outputs when terminating — and, on the other hand, from interactive systems, which continuously interact with their environment, but at their own rate (e.g., operating systems). Most industrial “real-time” systems are reactive — control, supervision and signal-processing systems — but other examples concern communication protocols or man-machine interfaces.