XML Vocabularies for Large Systems - 3 Philosophically Different Approaches

["Roger L. Costello" <costello@mitre.org>]

Hi Folks, 
 
I am interested in hearing about the nature of XML vocabularies that are
being created for large systems.  I am particularly interested in hearing
from people who have been successful in using simple XML vocabularies to
implement the complexities of varied data in large systems.  

Allow me to explain further...
 
DEFINITION
 
XML Vocabulary: an XML vocabulary is the collection of tags that is used to
markup data.  For example, this data:
 
     Borders Bookstore, 20 Boylston Avenue, Boston, MA, 01320
 
may be marked-up using this XML vocabulary:

     <Addressee>, <Street>, <City>, <State>, <Zipcode>.  
 
This later constitutes an XML vocabulary for U.S. Mailing Addresses.
 
SYSTEMS OF INTEREST
 
My interest is in large systems, where the variety of data is large, and
in the nature of XML vocabularies for such systems.
 
ISSUE - NATURE OF XML VOCABULARIES FOR LARGE SYSTEMS
 
I identify three philosophically different approaches to the creation of
an XML vocabulary for a large system:
 
   a. Create multiple, simple XML vocabularies.
   b. Create a single, simple XML vocabulary that is used in multiple ways.
   c. Create a single, large, complex XML vocabulary.
 
Let us examine each of these approaches:
 
a. Create multiple, simple XML vocabularies
 
   In daily life we encounter many analogues to this approach.  For example,
   the postal service has its own simple vocabulary - addressee, street,
   city, state, and zipcode; a restaurant has its own menu vocabulary - 
   appetizer, entree, dessert, and side dishes.  I am sure that you can 
   think of many other examples.  We live in a world filled with many 
   simple vocabularies, and (for the most part) we are able to move about 
   and function adequately with this multiplicity of simple vocabularies.
 
   Likewise, in creating an XML vocabulary for a large system one approach
   is to create multiple simple XML vocabularies.
 
b. Create a single, simple XML vocabulary that is used in multiple ways
 
   Consider the XML vocabulary called RSS.  It is a simple XML vocabulary.
   Despite its simplicity it is very popular and powerful.  Likewise, 
   Jabber is a very popular and powerful simple XML vocabulary.
 
   A second approach for the large system is to create a simple XML
   vocabulary that is used in multiple ways.  For example, you may  
   have an RSS feed that captures one aspect of the large system, 
   a second RSS feed that captures a second aspect of the large system, 
   and so forth.  The combination of RSS documents is used to 
   collectively capture all the data complexities in the large system.
 
c. Create a single, large, complex XML vocabulary
 
   All the complexities of the large system are implemented by creating a
   single, large, complex XML vocabulary.
 
QUESTIONS

Have you implemented a large system?  Have you created an XML vocabulary for
a large system?  Which of the above three approaches did you take? I am
particularly interested in hearing from people who have used simple XML
vocabularies [approach (a) or (b)] to achieve all the data complexities
in a large system.  
 
/Roger