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Re: RDF Concepts and Data Model document

From: <noah_mendelsohn@us.ibm.com>
Date: Tue, 24 Sep 2002 11:55:56 -0400
To: "Jonathan Borden" <jonathan@openhealth.org>
Cc: bwm@hplb.hpl.hp.com, skw@hplb.hpl.hp.com, tbray@textuality.com, timbl@w3.org, www-tag@w3.org
Message-ID: <OF5108BB4D.3A76B54B-ON85256C3E.005672C3@lotus.com>

With apologies in advance for commenting on a narrow point in a thread 
that I probably don't completely grok in the larger sense:

Experience with compound document systems suggests that we should indeed 
"go slow" in allowing embedded RDF to be interpreted independent of the 
semantics of its container.  My favorite compound document example is a 
fictitious word processor that chooses to keep it's "undo" list 
persistently in the document along with the current text.  Thus, assuming 
wp is the word processor's namespace, we get something like:

<wp:document>
  <wp:currentContent>
     ...real stuff here..
     <rdf:xxx ...probably describes the real stuff../>
  </wp:currentContent>

  <wp:deletedStuff>
      ...stuff that used to be in the document..
      <rdf:xxx ...probably describes the stuff that's
          no longer in the document../>
  </wp:deletedStuff>
</wp:document>

Let's say that my document used to say that the author was Noah, and the 
editing tool was smart enough to capture that in an RDF assertion.  Now I 
change my mind and delete that statement of authorship from the document. 
The RDF (probably) goes to the undo list, so that it can reappear if I 
issue an "undo".  It would clearly be a mistake to trust that RDF as 
representative of the current state of the document.

Of course, you could require that the application either edit the RDF to 
assert "we used to think Noah was the author but we don't think so now", 
or to use a non-RDF representation.  I think that, in general, such 
approaches reduce the power of XML.  Let's say I use XML to dump a 
database that contains XML fragments in various records.  Further assume 
some of that XML contains RDF assertions.   Should it be the 
responsibility of the dump program to rewrite those assertions to say: 
these assertions don't relate to the dump format container, they relate to 
the database records from which the dump was taken?  I don't think so.

All of the successful hierarchical compound document systems I know give 
outer structures relatively complete control over the semantics of 
anything contained within.  I suggest great caution if any other approach 
is tried with embedded RDF.

Again, apologies if my lack of understanding of RDF nuances has somehow 
reduces the usefulness of this comment.

------------------------------------------------------------------
Noah Mendelsohn                              Voice: 1-617-693-4036
IBM Corporation                                Fax: 1-617-693-8676
One Rogers Street
Cambridge, MA 02142
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Received on Tuesday, 24 September 2002 11:59:39 GMT

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