Locking without requesting a lock: A consistency maintenance mechanism in Internet-based real-time group editors

Consistency maintenance is an important issue in groupware systems. This article proposes an exclusive version locking scheme for consistency maintenance in Internet-based real-time collaborative editing environments. With this scheme, it is not necessary to propagate lock requests over the network. Locks will be automatically enforced by the system in a distributed way. The scheme supports concurrent editing on the same object by multi-versioning. Individual users’ concurrent conflicting intentions are thus accommodated in different versions. Meanwhile, each version is guaranteed to be exclusively locked by one user such that conflict resolution processes among users can be facilitated. Several version locking protocols are also defined to preserve the atomicity of a user's multiple intentions on the same object. The scheme and protocols have been implemented in a research prototype called POLO.