Giving undo attention

The problems associated with the provision of an undo support facility in the context of a synchronous shared or group editor are investigated. Previous work on the development of formal models of ‘undo’ has been restricted to single user systems and has focused on the functionality of undo, as opposed to discussing the support that users require from any error recovery facility. Motivated by new issues that arise in the context of computer supported co-operative work, the authors aim to integrate formal modelling of undo with an analysis of how users understand undo facilities. Together, these combined perspectives of the system and user lead to concrete design advice for implementing an undo facility. The special issues that arise in the context of shared undo also shed light on the emphasis that should be placed on single user undo. In particular, the authors regard undo not as a system command to be implemented, but as a user intention to be supported by the system.