A multi-version approach to conflict resolution in distributed groupware systems

Groupware systems are a special class of distributed computing systems which support human-computer-human interaction. Real-time collaborative graphics editors allow a group of users to view and edit the same graphics document at the same time from geographically dispersed sites connected by communication networks. Resolving conflict access to shared objects is one of the core issues in the design of this type of system. This paper proposes a novel distributed multi-version approach to conflict resolution. This approach aims to preserve the work concurrently produced by multiple users in the face of conflicts, and to minimize the number of object versions for accommodating combined effects of conflicting and compatible operations. Major technical contributions of this work include a formal specification of a unique combined effect for any group of conflicting and compatible operations, a distributed algorithm for incremental creation of multiple object versions, and a consistent object identification scheme for multi-version and multireplica graphics editing systems. All algorithms and schemes preserved in this paper have been used in the GRACE (Graphics Collaborative Editing) system implemented in Java.