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.

Due to lack of full awareness of other users' intentions, the possibility of inadvertent mistakes is higher in collaborative work, and yet most current collaborative systems fail to provide adequate facilities for undoing actions. This limitation occurs because undo facilities of single-user systems do not readily apply to collaborative systems. In this paper, we propose a general framework for undoing actions in collaborative software systems. The framework takes into account the possibility of conflicts between different users' actions that may prevent a normal undo. The framework also allows selection of actions to undo based on who performed them, where they occurred, or any other appropriate criteria. 1 Introduction The ability to reverse, or undo, the effects of previous actions has become a common feature in modern application software. This ability is particularly valuable in collaborative applications, but it is technically much more difficult to implement than in a single-us...

The purpose of our project is to provide toolkits for building applications that support collaboration between people in distributed environments. In this paper, we describe one such toolkit, called DistEdit, that can be used to build interactive group editors for distributed environments. This toolkit has the ability to support different editors simultaneously and provides a high degree of fault-tolerance against machine crashes. To evaluate the toolkit, we modified two editors to make use of the toolkit. The resulting editors allow users to take turns at making changes while other users observe the changes as they occur. We give an evaluation of the toolkit based on the development and use of these editors.