Content Type for XML Objects

I have received a request to assign an Object Identifier (OID) to be 
used as a content type for XML objects.  The idea is that one would 
look inside the XML object to determine  the type of XML object that 
is being carried inside CMS.
Is this the right thing to do?

Would it be better to have a different content type for each XML object?

Would it be better to use id-data?

Russ