A unified computational model called GroupSPACE is presented for groupware applications of repetitive-collaborative tasks in Computer Supported Cooperative Work (CSCW). GroupSPACE is a generalisation of the concept of workspace. It is inherently a distributed multimedia environment that provides specialised elementary composition and synchronisation operations on multimedia objects placed into this shared-space environment. Different views (viewpoints) of media objects and their relations are defined. According to their viewpoints, human users of GroupSPACE interact via direct manipulation on multimedia objects of GroupSPACE. The means by which different media objects are related, the control within GroupSPACE, is described by objects that can also be manipulated directly because the architecture of GroupSPACE is based on the paradigm of computational reflection.

Group communications is an area of research which has received a lot of atten-tion recently. This paper focuses on a model and the architecture of a system which supports group communications by providing group and session management function-ality. This system is an extension of directory services which are used with unicast communications. New functionality is needed for the dynamics of group communica-tions �members of a connection may change over the lifetime of the connection � and increased complexity ofrelations. A model is described which de�nes six object types which represent the relevant objects. Users and groups represent real world users and their relations. Sessions and �ows describe ongoing group communications. Flow tem-plates and certi�cates provide mechanisms for management and security issues. The architecture presented in this paper is transport-independent, ie it can be used within di�erent group communication platforms. A short sketch of the implementation is given in the last section. 1.

: Current approaches to CSCW application support are limited by their failure to support application distribution, internal application concurrency, anonymous communication, easy application integration, and run-time application behaviour modification. This paper argues that these limitations may be addressed at the language level. Accordingly, we introduce a new model and language which assimilates CSCW requirements as features tailored to the construction of open systems. KEY WORDS: CSCW, Composition 1 Introduction "Every interesting concurrent system is built from independent agents which communicate " [Milner, 1992] C OMPUTER Supported Cooperative Work is the field concerned with how people collaborate on any given task, and how computer applications, called groupware applications, may be developed to augment and better facilitate this process. It reflects a change in emphasis from the traditional use of the computer to solve problems to using the computer to facilitate human ...

Open distributed systems we are going to conceive in the future will present challenging design and operating requirements demands. Integrating dynamically autonomous distributed modules, allowing module reuse, coping with specific user requirements, such as QoS, are going to be common tasks a designer will have to face. In this context, it is convenient to make available suitable models to design such systems and provide flexibility to handle dynamic requirements.