Understanding the 2-way and 3-way compare modes

Two-way compare

You can turn on two-way compare by selecting the Two-Way Compare (Ignore Ancestor) button in the Text Compare toolbar. In a two-way comparison, the comparison is only between the two latest revisions of the branched object in the two DRM versions. In a two-way comparison, all changes are in gray. Changes in gray are applied automatically upon selection of the Copy Current Change from Left to Right. That is to say, changes in the left pane will be used to replace content in the right pane.

Three-way compare

This feature is most useful when merging objects that have conflicting changes (the object is listed in the Conflict folder of the DRM Synchronization view). If a common ancestor of a branched object is available, the Text Compare view allows for a three-way comparison. You can display the common ancestor in a three-way compare by selecting the Show Ancestor Pane button in the toolbar of the Text Compare view.

Three-way comparisons show the differences between three different revisions of a branched object:
  • The common ancestor revision of the branched object.
  • The revision of the object in the source DRM version.
  • The branched or cloned object in the target DRM version.
The relationship between the three revisions of the object can be seen using the DRM Graph Clone Tree view, as shown in the following diagram:
Three-way compare
The diagram shows the Text Compare view and DRM Graph Clone Tree view. The views are opened for a three-way comparison of a branched topic, Shoveling Snow. In the top pane of the Text Compare is the common ancestor revision, revision 1. This same revision is shown in the yellow box in the DRM Graph Clone Tree view. Revision 1 is the common ancestor of revision 2 of the same branch, DRM version 1.0, as well as revision 4 of the branch in DRM version 1.1.
In a three-way compare the Text Compare view shows you:
  • What has been changed in the first child (revision 2 in DRM version 1.0) in comparison to the common ancestor (revision 1).
  • What has been changed in the second child (revision 4 in DRM version 1.1) in comparison to the common ancestor (revision 1).
The differences that are highlighted are:
  • What has changed in revision 2 in DRM version 1.0 as compared to the common ancestor
  • What has been changed in revision 4 in DRM version 1.1 as compared to the common ancestor.

The sections that differ in all three revisions are highlighted as differences. Conflicts are shown in red and changes that will be applied are in gray. Conflicts must be manually resolved (that is, the conflict content in the left pane will simply be copied to the right and the content in the right will NOT be automatically removed). Changes in gray are applied automatically upon selection of the Copy Current Change from Left to Right.

A three-way comparison lets you find where pieces of content between the two revisions are different (i.e., the content is in conflict) so that you can merge them manually. These are the types of changes shown in red in the Text Compare.