Object Coherence in Distributed Interaction

Realtime distributed groupware (RDG) systems use computers and networks to support geographically separated users in their work on a common task at the same time. An RDG session typically consists of two types of interaction — that which involves one or more shared objects, and the use of audio-visual conferencing. It is important for users of such systems that the responsiveness of their interaction with shared objects has the same immediacy as their audio-visual communications. At the same time shared objects must have their integrity guarded in the face of multiple concurrent readers and writers. These coherence and responsiveness requirements often pull implementations in opposing directions. The concept of interactive atoms is introduced to address this problem. The successful construction of a distributed shared multi-user spreadsheet using multicast-based interactive atoms and multicast-based audio-visual channels is described.