A base model is the common ancestor for the versions of a model being compared or merged, and is used to track differences between model versions.
When you compare three models, you select a base model for the two versions of a model being compared.
When you compare two models, either you compare a version of a model with its base model, or two versions of a model that have the same base model.
Parent topic: Model roles in a compare and merge session
Related concepts
Differences between versions of a model
Merged models
Composite models
Related tasks
Comparing two or three versions of a model in a ClearCase environment