Coordination of Systems with Real-Time Properties in Manifold George A. Papadopoulos † Department of Computer Science University of Cyprus 75 Kallipoleos Str, P.O.B. 537 CY-1678 Nicosia, Cyprus E-mail: george@turing.cs.ucy.ac.cy Farhad Arbab Department of Interactive Systems Centre for Mathematics and Computer Science (CWI) Kruislaan 413, 1098 SJ Amsterdam The Netherlands E-mail: farhad@cwi.nl Abstract This paper combines work done in the areas of asynchronous timed computations and coordination models in order to derive a framework able to express real-time coordination without adhering to special architectures or real-time programming languages. In particular, it is shown how the coordination language MANIFOLD can be used to support coordinators with bounded response time. The only assumption made about the coordinated components is that they adhere to some constraints as imposed by timed asynchronous computational models derived for concurrent constraint languages. The model can be used as a basis for building complex software and hardware systems with the distinct advantage of enhancing reusability of existing components. Indeed, it is already being used in a project aiming to develop distributed multimedia applications. Keywords: Real-Time Coordination; Timed Asynchronous Languages; Reactive Systems; Software Development for Distributed and Parallel Processing Systems; Interoperability in Systems and Tools; Large-Scale Software System Integration. 1 Introduction The concept of coordinating a number of activities, possibly created independently from each other, such that they can run concurrently in a parallel and/or distributed fashion has received wide attention and a number of coordination models have been developed ([3]). Most of the proposed coordination frameworks however are suited for environments where the sub-components comprising an application are conventional ones in the sense that they do not adhere to any real-time constraints. Those few that are adressing this issue of real-time coordination either rely on the ability of the underlying architecture apparatus to provide real-time support ([7]) and/or are confined to using a specific real-time language ([6]). However, all the issues pertaining to † This work was done while the author was visiting CWI as part of the ERCIM-HCM Fellowship Programme financed by the Commission of the European Community under contract no. ERBCHBGCT930350. conventional coordination frameworks are still valid in those exhibiting real-time properties. Even more, the use of a separate coordination formalism with real-time capabilities “gluing together” real-time (software and/or hardware) components helps in separating issues related to specifying the computational part of the components from those concerned specifically with their real-time behaviour ([7]). In this paper we address the issue of real-time coordination but with a number of self imposed constraints which we feel, if satisfied, will render the proposed model suitable for a wide variety of applications. These constraints are: • The coordination model should not rely on any specific architecture configuration supporting real-time response and should be implementable on a variety of systems including distributed ones. • Language interoperability should not be sacrificed and the real-time framework should not be based on the use of specific language formalisms. In addition, the proposed framework should be able to enjoy the properties of state-of-the-art coordination models proposed for conventional (non real-time) environments but also address issues peculiar to the presence of real-time behaviour such as the separation of the computational part of an application from that of real-time coordination. We attempt to meet the above mentioned targets by combining work done in the area of coordination models with that done for asynchronous timed computations. Our starting points are the coordination event-driven language MANIFOLD ([1,2]) and the tcc computational model ([8]) developed for concurrent constraint languages. More to the point, we show how MANIFOLD coordinators can exhibit real-time behaviour in the sense that reaction to events can always be done in bounded time, even if not instantaneously. This combination yields a coordination environment exhibiting real-time properties without imposing any difficult to meet constraints on the implementation of the programming languages used or the underlying architecture. 2 The IWIM Model and the Language MANIFOLD Most of the message passing models of communication can be classified under the generic title of TSR (Targeted- Send/Receive) in the sense that there is some asymmetry in