CompoundIdentifier is a class that enables associating one or more unique identifiers (plus information regarding the creator of the identifiers) to the various objects in the application data model. Compound identifiers will be used by every class that needs to "stand alone" and be referenced by other objects.
A unique (integer, locally-scoped) ID for a particular instance of an object.
Can be created in a distributed fashion (i.e., without a centralized naming authority, as long as there is reasonable certainty of its uniqueness. Note that a given object can be associated with multiple unique IDs.
Example (represented as XML) of something that has two unique identifiers for it, each produced by a different source.