The Unified Backend does not manage topic map data itself, instead it provides a view onto multiple topic maps managed by any of the other backends. That view presents the multiple topic maps as if they were merged into a single topic map. This view is a read-only view, although the topic map objects from the underlying backends are accessible through additional APIs in the Unified Backend, allowing an application to "reach in" to one of the underlying topic maps and modify it.
Currently the Unified Backend does not implement the Topic Naming Constraint, which requires that topics with the same name in the same scope get merged. However, topics with the same subject address or subject indicator address will be exposed as a single merged topic in this view.
The Unified Backend can be useful to layer one topic map on top of another e.g. for annotation purposes, without requiring the physical creation of the merger of the two maps.