ExternalIdentifier overlap with external classifications

In retrospect an ExternalIdentifier is just like an external
classification where the taxonomy is an identification taxonomy instead
of a classification taxonomy. Another way to look at it is that
identification is a form of classification. Imagine DUNS being a
classification scheme and all the companies (Iona, Stirling Commerce,
...) are just nodes in a classification tree rooted under DUNS scheme.

By treating external identification by re-using classification we can
remove ExternalIdentifier all together but keep a separate method for
getting identifiers in RegistryObject. Alternatively we could keep it
but make it 2 empty sub-classes of Classification and
ExternalClassification propose in a previous email. See:


http://lists.oasis-open.org/archives/regrep-ex-scheme/200109/msg00000.html

for details.

Other Problems with current ExternalIdentifier
-----------------------------------------------
A related matter is that the ExternalIdentifier class currently does not
have adequate attributes. An external identifier needs to have its
identification scheme defined by a ClassificationScheme (internal or
external). Currently the name attribute provides that info. But we need
a
human friendly name for each external identifier. Take the example where
Sun is identified under DUNS with name Sun and value "123". Current
ExternalIdentifier witll use its name attribute for "DUNS" to identofy
scheme and value would be "123" leaving no place for user friendly name
"Sun".

Summary
----------
By removing or sub-classing ExternalIdentifier we not only make it
possibloy for an external id to be based on an internal or external
coding scheme we also fix some bugs with current model.

--
Regards,
Farrukh