In this paper we argue that a programming language for real-time systems should support the declaration of timeconstraints, and that those constraints should attach to a well-developed notion of reactions. To make our claims more precise, we introduce Timber, which is a concurrent programming language based on a model of non-blocking, reactive objects. Timber supports both upper and lower time constraints on a reaction, where an upper constraint corresponds to a classical deadline, and a lower constraint constitutes a very efficient way of scheduling an event to occur at a well-defined point in the future. A series of programming examples illustrates how these mechanisms can be used to express simple solutions to common problems in practical real-time programming. 1.

Abstract. This paper is devoted to the presentation of the key concepts on which a mathematical theory of complex (industrial) systems can be based. We especially show how this formal framework can capture the realness of modern information technologies. We also present some new modelling problems that are naturally emerging in the specific context of complex software systems.