Multiple vocabularies
Meaning of terms may be same, similar or different:
  - Different terms, same meaning
    
      - Not such a
problem
- Rule can
say <DocumentCreator> is the same as <Author>
 
- Same terms, different meaning
    
      - Ambiguity
- Is  <DocumentCreator>  the person or the
organization that the created the document?
- Much bigger
problem
 
- Different terms, related meaning
    
      - How do meanings relate?
- If I
understand  <PlaneTicket> , what can I
understand about  <NonRefundablePlaneTicket> ?