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Re: issue-mt-ns : XML is not RDF

From: Sean B. Palmer <sean@miscoranda.com>
Date: Thu, 2 Nov 2006 19:52:36 +0000
Message-ID: <b6bb4d890611021152y1902a42dxe9caf14a15bf756c@mail.gmail.com>
To: "Danny Ayers" <danny.ayers@gmail.com>
Cc: "Dan Connolly" <connolly@w3.org>, public-grddl-wg <public-grddl-wg@w3.org>, www-archive@w3.org

> This may be ok, but as it stands steps outside the grddl-wg's remit
> into TAG and (unchartered) RDF group's territory.

Actually it doesn't. From a corollary of the definition of
application/xml in RFC 3023, it can be demonstrated that someone
publishing an RDF/XML document as application/xml is asserting the
triples therein.

The argument is that the following:

[[[
   An XML document labeled as text/xml or application/xml might contain
   namespace declarations, stylesheet-linking processing instructions
   (PIs), schema information, or other declarations that might be used
   to suggest how the document is to be processed.  For example, a
   document might have the XHTML namespace and a reference to a CSS
   stylesheet.  Such a document might be handled by applications that
   would use this information to dispatch the document for appropriate
   processing.
]]] - Section 3, http://www.ietf.org/rfc/rfc3023.txt

Means that it is appropriate for a user agent to interpret an RDF/XML
document served as application/xml as RDF based on the namespace of
the root element. Since such a behaviour is allowed, it follows that
an author/publisher of such a document must expect the triples therein
to be taken as asserted; therefore they are asserted.

See http://lists.w3.org/Archives/Public/public-grddl-comments/2006OctDec/0019

> Content-Type: application/xml
>
> <html xmlns="http://www.w3.org/1999/xhtml "
> [...]
> XHTML, RDF/XML or both?

XHTML.

> Keying off the root element narrows things down considerably, but
> then RDF/XML doesn't mandate a specific root element.

No, but this is an application/xml document. You must interpret it per
the application/xml specification, which says that one may dispatch by
following the namespace mechanism, whereby it is an XHTML document by
root namespace dispatch. It doesn't say that you may use random
heuristics; therefore it cannot be an RDF/XML document.

You can think of this as being an analogy to
rdfms-qnames-cant-represent-all-uris. The RDF syntax can't model all
possible RDF graphs. Likewise, neither can application/xml be the
carrier type for all possible syntactically valid application/xml
documents. Unlike with the former problem, however, there is a
workaround: just use application/rdf+xml!

It could be argued that root namespace dispatch isn't documented as
being the primary mechanism for namespace dispatch, but it seems
common sense given that the root element encapsulates the entire rest
of the document; moreover I would consider there to be overwhelming
tool support for it, and consensus amongst specificationeers seems to
be converging upon it.

Cheers,

-- 
Sean B. Palmer, http://inamidst.com/sbp/
Received on Thursday, 2 November 2006 19:53:07 GMT

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