Three-way Merge

Note

For full details on branching and merging, please refer to the appropriate section in the Simcenter System Simulation Client for Git documentation.

Simcenter System Simulation Client for Git, like other modern role-based access collaborative versioning systems, allows users to create branches. These branches allow users to use a single model (or collection) as the basis for their work, and develop it according to their own needs, often in differing and diverging directions.

There are numerous advantages to this, not least of which is the ability to isolate your work from that of your colleagues. However, a common requirement is also to take two branches which have been worked on independently, and to merge them.

This is equivalent to taking the changes made in one branch, and transferring them to the other, allowing both branches to converge.

Figure 366: Merging

The schematic above illustrates a common example of a merge scenario between two branches, Source and Target.

The user in this instance is attempting to merge changes from Source V2 into Target V3. The merged version will be saved as Target V4.

For the purposes of the merge operation, a three-way comparison is made between:

• The local version (in this case, Target V3, into which changes are being merged). This is also referred to as mine in common terminology.

• The remote version (in this case, Source V2, from which changes are being merged). This is also referred to as theirs in common terminology.

• The base (sometimes called reference) version, which is a common ancestor of the local and remote versions. This is the closest version in the branch system from which both local and remote have both originated.

If both local and remote versions differ from each other and they both differ from the base version, then a conflict has occurred in the merge process.

This conflict can occur at the level of any of the elements being merged. For Simcenter Amesim models, the granularity is that of the Model Comparison tool, i.e:

• Model structure: presence/absence of components and connection lines

• Global parameter values

• Submodels set for a given component

• Presence/absence of parameters as a result of submodel differences

• Parameter values and titles

There are automated ways of resolving merge conflicts provided you can always merge in favor of one side or the other, i.e. copying all the conflicted changes from one side to the other.

However, there are more nuanced ways of merging conflicts which is to choose specifically which side to copy changes from for each instance of a conflict. This is where Three-way Merge comes in.