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Are we elements or animals? (was: Use of fragment identifiers in XML)

From: Aaron Swartz <me@aaronsw.com>
Date: Thu, 31 Oct 2002 17:45:12 -0600
Cc: Dan Brickley <danbri@w3.org>, Brian McBride <bwm@hplb.hpl.hp.com>, "Simon St.Laurent" <simonstl@simonstl.com>, www-tag@w3.org, Chris Lilley <chris@w3.org>
To: Dan Connolly <connolly@w3.org>
Message-Id: <CC6FC9CC-ED2A-11D6-8DD8-003065F376B6@aaronsw.com>

On Thursday, October 31, 2002, at 05:07 PM, Dan Connolly wrote:
> But I'm sure I've seen test cases where this one matters. [...] But I 
> can't seem to bring it to mind. It was something about using the same 
> URI in XLink and RDF, in such a way that the XLink seems to refer to 
> an element and the RDF seems to refer to what the element is talking 
> about.

Are you thinking of XPointer?

RFC2396: "The semantics of a fragment identifier [...] is dependent on 
the media type \[RFC2046\] of the retrieval result."

RFC2046: "Additional character sets may be registered with IANA."

http://www.iana.org/ -> http://www.iana.org/numbers.html -> 
http://www.iana.org/assignments/media-types/index.html -> 
http://www.iana.org/assignments/media-types/application/ which says:

"xml [is registered in] \[RFC3023\]"

RFC3023:
    XML Pointer Language (XPointer)", attempts to define fragment
    identifiers for text/xml and application/xml.  The current
    specification for XPointer is available at http://www.w3.org/TR/xptr.

http://www.w3.org/TR/xptr -> http://www.w3.org/TR/xptr-framework/ which 
now has weasel words about RDF and SOAP, but still says:

"This specification defines [a framework which] is intended to be used 
as a basis for fragment identifiers for any resource whose Internet 
media type is one of text/xml, application/xml, 
text/xml-external-parsed-entity, or 
application/xml-external-parsed-entity."

"The Name identifies a single element in the XML resource by ID"

Conclusion: RDF documents which describe fragments *cannot be safely 
served* as application/xml.

(The W3C serves *all* of its RDF documents with that mime type! All of 
TimBL's carefully RDF-specified ...w3.org...#dogs and ...#cats turn out 
to be elements, not animals.)

-- 
Aaron Swartz [http://www.aaronsw.com] "Curb your consumption," he said.
Received on Thursday, 31 October 2002 18:45:13 UTC

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