Supporting semantic maintenance of complex Undo operations in replicated Co-AutoCAD environments

In order to bridge the gap between complex operations and atomic operations in CAD groupware, adapter tools are introduced to decompose complex operations into atomic ones by breaking up the former according to different steps and different objects. However, during the decomposition process, because of the loss of the relationships between the original operations and the atomic ones, the intention of the Undo operation of the complex operation may be violated by concurrent operations coming from remote sites since traditional Undo schema is based on the decomposed operation history buffer and the undo unit is the atomic operation. The paper discusses the problems of Undo pre-condition and Undo conflict, and introduces Original Op history buffer and Bi-Vector strategy to maintain the relationship between the original operations and the decomposed ones. Moreover, the paper gives detailed description about the work flow and main algorithms of complex Undo operations. Examples are given to demonstrate the effectiveness of our strategy.