A framework for undoing actions in collaborative systems

The ability to undo operations is a standard feature in most single-user interactive applications. We propose a general framework for implementing undo in collaborative systems. The framework allows users to reverse their own changes individually, taking into account the possibility of conflicts between different users' operations that may prevent an undo. The proposed framework has been incorporated into DistEdit, a toolkit for building group text editors. Based on our experience with DistEdit's undo facilities, we discuss several issues that need to be taken into account in using the framework, in order to ensure that a reasonable undo behavior is provided to users. We show that the framework is also applicable to single-user systems, since the operations to undo can be selected not just on the basis of who performed them, but by any appropriate criterion, such as the document region in which the operations occurred or the time interval in which the operations were carried out.