DESCRIBING OPEN DISTRIBUTED SYSTEMS - A FOUNDATION

In this paper we outline a semantic model for open distributed systems which provides a foundation for a corresponding architecture descript ion language, This semantic model is based on reported architecture mo dels, with a number of refinements to support abstraction and composit ion, The model is specifically designed to describe open distributed s ystems independently of implementation details such as communication p rotocols and middleware systems, The modelling concepts in the semanti c model are: object (a model of an entity), event (a unit of interacti on between an object and its environment), event relationship (a speci fication of behaviour defining the relationships amongst a set of even ts), interface (an abstraction of an abject's interaction with its env ironment) and binding (a context for interaction between objects), The binding concept is particularly important because it can describe any kind of interaction in an open distributed system, ranging from remot e procedure calls and multicast to more complex, enterprise interactio ns, Special attention is given to the problem of composition and abstr action of events and behaviour in the model, This is needed to reflect the reuse, evolution and interworking requirements of open distribute d systems, Our approach allows for the effective modelling of asynchro ny, concurrency and complex hows of information in open distributed sy stems.