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Re: Internal DTD Examples Invalidate the RDF/XML Documents

From: Frank Manola <fmanola@acm.org>
Date: Thu, 02 Oct 2003 10:28:08 -0400
Message-ID: <3F7C35F8.2050503@acm.org>
To: dennis.hamilton@acm.org
Cc: www-rdf-comments@w3.org

Hi Dennis--

The use of internal DTD subsets in these Primer examples was merely to 
illustrate the use of entities as an abbreviation mechanism.  It 
*wasn't* intended to suggest that ordinary XML validation should be 
applied to RDF/XML.  RDF/XML requires that the XML be well-formed, but 
it doesn't require that the XML be valid, and ordinary RDF/XML parsers 
and validators don't use DTDs or XML Schemas to do XML validation on the 
RDF/XML (the Primer examples are valid RDF/XML according to the W3C RDF 
validator).  Moreover, it's perfectly OK to use internal DTD subsets to 
define entities in XML you don't intend to validate (there's a 
well-formedness constraint in the XML spec that covers this situation) 
and, technically, RDF/XML *without* a document type declaration isn't 
valid, so it isn't exactly the introduction of an internal DTD subset 
that causes the RDF/XML to be invalid.

It's been known for some time that the current grammar of RDF/XML isn't 
amenable to description in a DTD (or an XML Schema).  Producing such a 
grammar was considered by the RDF Core WG, but it was decided that the 
changes would be so extensive as to be outside the current WG's charter. 
    This has been added to the RDF Core postponed issues list at:

http://www.w3.org/2000/03/rdf-tracking/#rdfms-validating-embedded-rdf

We also received related Last Call comments on this subject labeled as 
xmlsch-10 and xmlsch-12, which can be found at
http://www.w3.org/2001/sw/RDFCore/20030123-issues/

Do you feel this issue needs additional discussion (in the Primer or 
some other RDF spec)?

--Frank


Dennis E. Hamilton wrote:

> I have been reading over the current RDF Primer Working Document, 
> 
> 	<http://www.w3.org/TR/2003/WD-rdf-primer-20030905/>
> 
> And I notice that the introduction of internal DTD subsets to provide entity definitions (e.g., for &xsd;) results in the XML document being [DTD] invalid.
> 
> The problem is that there are no markup declarations so not even the <rdf:RDF> root element is valid.  
> 
> First, unless you also want to suppose a mythical external DTD, as in
> 
> <!DOCTYPE rdf:RDF SYSTEM "http://example.com/example.dtd"
> 	[ <!ENTITY xsd "http://www.w3.org/2001/XMLSchema#"> ] >
> 
> the example just doesn't work.
> 
> Second, making a valid DTD for an RDF/XML document is an interesting challenge, so maybe one shouldn't even go down this road.  *I* like the idea, but I tend to be anal about creating DTDs, even if it means I must maintain the RDF/XML and a unique DTD for it side-by-side.
> 
> -- Dennis
> 
> Dennis E. Hamilton
> ------------------
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Received on Thursday, 2 October 2003 10:06:42 GMT

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