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   RDF not conforming to the Namespace spec?

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  • From: "Roger L. Costello" <costello@mitre.org>
  • To: xml-dev@ic.ac.uk
  • Date: Thu, 11 Mar 1999 07:18:59 -0500

Hi Folks,

There has been a lot of discussion on this list group about namespaces
and how there is no necessary link between a namespace URI and a schema
(DTD).  Just as I was accepting that and getting comfortable with it I
read the RDF spec...

For those of you unfamiliar with RDF, its mission in life is to enable
you to express data about your data; i.e., metadata.  You can express
things like, "the creator of the BookCatalog is John Doe".  "creator" is
a piece of metadata about the "resource", BookCatalog.  In RDF "creator"
is called a "property".  Thus, the "property" <creator> has the "value"
John Doe ...  <creator>John Doe</creator>.

Okay, here's where the rub comes.  Let me give you a couple of quotes
from the RDF spec (the *'s I have put in and are my way of emphasizing
the words that I wish for you to really focus on):  "Property names
*must* be associated with a schema.  This can be done by qualifying the
element names with a namespace prefix to unambigously *connect* the
property definition with the corresponding RDF schema ..."  Earlier in
the spec it says: "Due to RDF's incremental extensibility, agents
processing metadata will be able to trace the origins of schemata they
are unfamiliar with back to known schemata and perform meaningful
actions on metadata they weren't originally designed to process."

Let me tell you how I interpret those two sentences.  Suppose that I
haver written a Web agent and it comes across a Web site that serves up
an XML document containing some metadata (expressed using the RDF
syntax).  Let's suppose that the metadata says, in XMLese, "the creator
of the BookCatalog is John Doe".  My agent has never seen the property
"creator", so it follows the namespace URI to the property schema.  From
there it finds the superclass of the creator property.  If it doesn't
recognize that class then it goes to its superclass.  It keeps doing
this until it finds a class that it understands and then it starts
unwinding (presumably by this process it will be able to gain insight
into what "creator" is all about.  I have no idea how this will happen,
but it sounds pretty cool.)

This mechanism of following references until the agent gains
"enlightenment" makes sense to me.  I like it!  ***However*** that
presupposes that there is a *guaranteed* association between a namespace
URI and a schema.  This is totally against what this list group has
worked so hard to clarify as NOT being the case.

Somebody help me to understand this.  Obviously I am misreading,
misinterpreting the RDF spec.  Thanks.  /Roger

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