Grouping/Ungrouping in Graphical Collaborative Editing Systems

Often collaborative graphical systems lag behind in features with well accepted single-user applications. The frequently used operations of group/ungroup offered by almost every single-user graphical editor have not been considered by the collaborative graphical editing systems. In this paper we present an algorithm for consistency maintenance in collaborative graphical editing dealing not only with simple operations such as create, delete, move, change colour or position, but also with group/ungroup operations. The system relying on this algorithm is customizable, offering three policy modes for dealing with conflict: null-effect based policy, priority based policy and multi-versioning based policy.