What Is Design History?
Design history allows users to better manage the design process. It provides a complete revision control system that allows users to track and view the incremental changes made to a model. You can restore elements to a prior state through a combination of undoing and redoing historic changes.
Changes can be tracked down to the element level. To help track the revisions, each is identified with a revision number, file name, date and time, author, description of the change, and tags. While the revisions are attributed to a single author, the changes can be viewed and restored from a wide range of combinations. Because the logic for combinations of selection sets, multiple revisions, and undoing and redoing can be quite complex, the examples given deal with straightforward usage.
A revision records the difference between the current state of the model and the last revision saved. Only the difference is saved in the design history area of the DGN file, which minimizes additional storage requirements for history. Design history records changes in a linear fashion, from when design history was initialized to the present. Branching is not currently supported.
When enabled, design history becomes part of the DGN file. MicroStation PowerDraft preserves the integrity of history as carefully as it does ordinary elements, therefore design history serves as a reliable audit trail. By default, revisions cannot be removed from the design history of a file and there is no way to modify historical information. However, the MS_DESIGN_HISTORY configuration variable can be used to control modifications and deletions of design history.
The design history is maintained even when you save the DGN file with a different name (using Within the Design History dialog, this is indicated as a change in the design filename. All other items in the design history are unchanged.).
Once a revision has been committed, there are a number of viewing and recovery options. You can: