Linking an RDF instance to its RDF Schema

Hi All,

Working with protege recently, It can generate both an RDF
Schema and separate instance documents conforming to the 
schema; however, there is no direct, explicit link between the RDF Schema and 

its instance document.  Why not?  

I notice that the RDF Schema spec and the Primer are both silent on 
this issue.  As this is different than the process for XML documents, 
I would think an explanation or justification is in order.

Regards,

 - Mike
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Michael C. Daconta
Director, Web & Technology Services
www.mcbrad.com