Concurrent operations in a distributed and mobile collaborative environment

In a distributed groupware system, objects shared by users are subject to concurrency and real time constraints. In order to satisfy these, various concurrency control algorithms have been proposed that exploit the semantic properties of operations (C.A. Ellis and S.J. Gibbs, 1989; A. Karsenty and M. Beaudouin-Lafon, 1993; C. Sun et al., 1996). By ordering concurrent operations, they generally guarantee consistency of the different copies of each object. However, in some situations they can result in inconsistent copies, a non respect of user's intentions, and in the need to undo and redo some operations. The principle objective of the paper is to present an algorithm that overcomes these drawbacks in distributed and mobile collaborative environments. The algorithm is based on the notion of user intention, and also on the construction of equivalent histories by exploiting and combining some general semantic properties such as forward/backward transposition.