Currently in the model, the class VERSION_REPOSITORY defines an
object whose job it is to maintain a stack of versions of a single
logical object, such as a COMPOSITION, in the same way as an "s." file
versions a normal file in SCCS, and a ",v" file in RCS. However, this
name is problematic in openEHR for at least 3 reasons:

• the word "repository" implies something large, like a database

• the descendants of this class are all named VERSIONED_XXX (rather
  than VERSION_XXX)

• the word "repository" conflicts with other uses of the same word
  in the specifications.