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Re: RDF in XHTML

From: Murray Altheim <altheim@eng.sun.com>
Date: Thu, 19 Apr 2001 13:31:24 -0700
Message-ID: <3ADF4B1C.DE700B53@eng.sun.com>
To: Ken MacLeod <ken@bitsko.slc.ut.us>
CC: RDF Interest <www-rdf-interest@w3.org>
Ken MacLeod wrote:
> 
> Murray Altheim <altheim@eng.sun.com> writes:
> 
> > Jonathan Borden wrote:
> 
> > > What is wrong with the approach of including <rdf:RDF> elements
> > > within XHTML defined by an XML Schema module for RDF?
> 
> > I hope I answered this in more detail in a message I just sent
> > off. There's no definition in XML that allows for well-formed
> > content *within* valid content. Either the entire document is valid
> > or its not. DTDs cannot deal with only part of the content being
> > checked. I'm not even sure if XML Schema can do this.
> 
> XML Schema can't, Eric van der Vlist spent a long time trying each of
> DTDs, XML Schema, RELAX, and Schematron, and later TREX for validating
> some of the "looser" but commonly expected modular extensions to RSS.
> *Just* RSS, which has constraints even further than RDF alone.
> 
> That may be exactly the problem with extent XML specs, there is no
> spec that allows for well-formed (or seperately validated) content
> within valid content.
> 
> I think this problem would be easily solved once the realization is
> made that that is *exactly* what we are asking for in several
> applications of XML.

Perhaps it would help if I could understand the rationale behind this.
What you're essentially asking for is the ability to validate a portion
of a document (ie., you want a contract on its validity), but other
portions of the document you don't care about "making any sense" (which
is all DTD validation does, markup-wise). 

Without trying to open any arguments here, this has always been my
difficulty with RDF: its design is such that the mixing of namespaces
and author-created elements and attributes means that validation using
conventional tools is either problematic or impossible. Why isn't this
considered a fault of RDF syntax, not a fault the rest of the markup
world? Doesn't this sound religious to anyone? RDF syntax could have
been designed differently, to "play well with others" in this sense.
My influence on the design of XTM was very specifically to make it
play well with others, and certainly its more verbose than RDF but
can easily be processed and validated using any of the available 
schema mechanisms. It uses a number of concepts of namespaces, but in
a way that doesn't impinge upon common DTD validation.

In XML Schema we have one of the most involved, complex, and well-though
out specifications (probably only in competition with Hytime), and yet
it cannot validate RDF. That seems a real problem, and nothing that 
(as has been noted) is in the realm of XHTML to solve. IOW, should this
community come up with a generalized solution for inclusion and/or
validation of RDF-in-XML, then XHTML 2.0 could simply adopt it. I don't
think either myself or the HTML WG has the expertise, bandwidth, or 
political muscle to even consider such a thing. 

Murray

...........................................................................
Murray Altheim, SGML/XML Grease Monkey     <mailto:altheim&#64;eng.sun.com>
XML Technology Center
Sun Microsystems, 1601 Willow Rd., MS UMPK17-102, Menlo Park, CA 94025

      the wood louse sits on a splinter and sings to the rising sap
      ain't it awful how winter lingers in springtimes lap -- archy
Received on Thursday, 19 April 2001 16:29:22 GMT

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