ROLL-BACK DURING REGENERATION IN A COMPUTER-AIDED DESIGN SYSTEM

A method and apparatus that keeps information on all entities that are created when a model is built in a CAD system, including an indication of which command causes each entity to be added to or taken from the model. From this information, the system can determine the state of the model at any given time during its creation, without having to regenerate commands that generated the model at the determined state. For each new command, only those entities that are newly created are added to the database. The entities each have a version field that allows the same data to relate to different versions of the model.