Baseline
A baseline is applied to a set of components within a stream and serves analogously to labels in base ClearCase. Streams are configured with the help of Baselines, which act as a foundation or root layer for the stream's configuration in UCM clearcase. The baseline holds the UCM Activities. Baselines apply the label on the versions.
A recommended baseline is a set of versions that have been identified as stable. This baseline establishes the current starting point for the project; when a developer rebases or joins a project, this is the baseline that is used as the foundation for the development (or child) stream, unless he specifies a different baseline to be used.
Composite baselines are a mechanism for grouping baselines into a collection. One baseline is designated as the composite, and other baselines become members of the composite.
Read more about this topic: IBM Rational ClearCase UCM