Currently the openEHR Common model supports Contributions whose
contents may be Compositions from other systems. However, it does
not cleanly support the synchronisation of Contributions from one
system to another, such that the source systems and Contributions
can be identified (there no problem in applying the content of a
remote Contribution to a target system, just in identifying the
originating Contribution).

In a distributed, caching EHR computing environment, these semantics
would be needed, in a similar way to synchronisation of change-sets
between instances of software configuration management software such
as Subversion or BitKeeper.

A version identification system is also needed to support globally
unique identification of versions in such a way that clashes are
avoided when copies, moves and merges are made.

Various anomalies in the existing models can be fixed by a proper
version identification scheme:

• demographic model - PARTY.reverse_relationships cannot just be
  a uid

• referencing of CONTRIBUTION from VERSION and vice-versa

• how a DV_EHR_URI relates to the various identifiers