How ClearCase Merges

It identifies the base contributor.

Next, it compares each contributor against the base contributor.

For any line that is unchanged between the base contributor and any other contributor, ClearCase copies the line to the merge output file.

For any line that has changed between the base contributor and another contributor, ClearCase performs a trivial merge by accepting the change in the contributor. Note, however, that depending on how you started the merge operation, ClearCase may copy the change to the merge output file. However, you can disable the automated merge capability for any given merge operation. If you disable this capability, you must approve each change to the merge output file.

For any line that has changed between the base contributor and more than one other contributor, ClearCase requires that you resolve the conflicting difference.

About Merging in UCM

During a deliver or rebase operation, the ClearCase merge algorithm involves the following versions:

The source contributors: one version from your development stream and one version from the target stream.

The base contributor: the common ancestor of the source versions.

The destination version: the merge output, which in a deliver operation becomes a new version in the target stream and in a rebase operation becomes a new version in the development stream.

About Merging in Base ClearCase

Contributors, which are typically one version from each branch you are merging. (You can merge up to 15 contributors.) You specify which versions are contributors.

The base contributor, which is typically the closest common ancestor of the contributors. (For selective merges, subtractive merges, and merges in an environment with complex branch structures, the base contributor may not be the closest common ancestor.) ClearCase determines which contributor is the base contributor. The target contributor, which is typically the latest version on the branch that will contain the results of the merge. You determine which version is the target contributor.

The merge output file or directory, which contains the results of the merge and is usually checked in as a successor to the target contributor. By default, the merge output file is the checked-out version of the target contributor, but you can choose a different file to contain the merge output.