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We describe the design of a system that supports a lecturer in preparing and performing education sessions in which the audience participates from remote locations via networked computers. Most current projects on "virtual classrooms" and "tele-teaching" focus on an straight-forward extension of the traditional class room model by broadcasting a lecture with video-conferencing technologies [MUN96][CAE96].
Our approach is different because we base it on the logical structure of a modern computer-supported education session. In our vision such a session is a concert of multiple software instruments that concurrently perform various tasks with the lecturer conducting their use and interaction. Audio may be one such instrument, a slide presentation another, the demonstration of an application program with the possibility of running interactive exercises by the audience is a third one.
In such a scenario, the application of video (while nice if available) plays a secondary role since most of a session's information contents is actually provided by the other software instruments. Consequently computer-based distributed education sessions may cope with much tighter constraints on network bandwidth than distributed classrooms fundamentally based on video technology.
However, organizing education sessions of this kind is a challenging task that requires the coordination of concurrent activities operating in real-time on objects of different types located in a distributed environment. Currently this is hardly feasible for computer experts with experience in network programming. Our goal is to break down the complexity of this task to the level of preparing an animated slide show with the help of the presentation tools available today.
Since technology is rapidly evolving with many competing systems and standards promoted by different vendors, the system design is based on an abstract reference architecture named CONCERT under which various technologies can be integrated and on top of which different coordination languages can be built. The CONCERT architecture can be implemented with realistic efforts in the mid-term future based on already available systems and technologies yielding an application framework i.e. an object-oriented software library into which application/system-specific components can be plugged.
The rest of this paper is organized as follows:
Appendix Technologies for Distributed Systems contains a review of relevant technologies that have influenced our design; we have also delegated most references to related work to this section.