Reducing the problems of group undo

Providing undo functionality in groupware has been identified as an important, but difficult problem. Existing solutions show deficiencies like lacking generality, being too complex, being inefficient, or failing to yield acceptable results in common situations. In this paper we describe a new approach which reduces local group undo to a transformation-based method for combining the effects of concurrently issued user commands. Besides transformations we introduce mirror and folding operators in order to build a unique and consistent multidimensional model of the user interaction. In this way the problems of group undo mentioned above can be either overcome or at least reduced.