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[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: RDF and RELAX NG
On Thu, 21 Aug 2003 21:12:44 -0400
"Simon St.Laurent" <simonstl@s...> wrote:
> Earlier this week, dave.beckett@b... (Dave Beckett) wrote:
well, a few weeks ago. I've been busy releasing RDF software[*] :)
> >As far as any XML schema language is appropriate for general RDF/XML
> >with it's open use of XML Namespaces, RelaxNG is the one I'd suggest is
> >most appropriate (compared to for example W3C XML Schemas which is more
> >of a closed/complete DTD style).
>
> This discussion has connected with a number of other conversations to
> leave me wondering whether RELAX NG might prove to be more than a schema
> language capable of of validating RDF/XML, but indeed a schema language
> which eases the conflicts at the boundaries between RDF and XML.
I've thought similar things myself.
> RDF/XML has taken a lot of flak lately. On the one hand, it offers too
> many options, so developers who want to work with RDF data using XML
> tools face a pretty frustrating task, even before getting into the risks
> of processing graphs with tree-oriented tools. On the other hand,
> trying to make XML vocabularies RDF/XML compatible is not much fun
> either. Some aspects of this [1] don't even seem like good markup
> practice to me, especially things like "eschew mixed content", the use
> of RDF-namespaced attributes in host vocabularies, and container issues.
The RDF/XML complaints are well known, even the unjustified ones :)
I didn't think all of [1] was particularly a good idea. Mixed content
in XML is a key feature and important for end-user markup. Although
it's transportable by RDF/XML, that's probably not the main point.
Where you want to essentially annotate some XML file/format and connect
it to an RDF approach, it seems better to give only a minimal change to
the "host" language. That tends to indicate either what could be
considered an XML schema annotation style or a match and transform
approach, something like using XSLT or Schematron.
> We can struggle along with this, sure. RDF and XML seem stuck in a
> lousy marriage at this point, each disappointing the other on a regular
> basis. Mark Pilgrim's done a nice job [2] of delineating various ways
> in which this conversation often flows, tying it to the
> Pie/Echo/Atom/etc. project's concrete challenges. It seems like there
> should be some way of at least separating those issues in practice.
>
> It may be very naive of me to think this, but something keeps telling me
> that RELAX NG's patterns and RDF's graphs may be able to talk to each
> other in ways that go well beyond the rdf:parseType attribute or XSLT
> transforms between attribute names in a local vocabulary and the rdf:ID,
> rdf:about, etc. I suspect (though I'm still working it out, and don't
> know nearly enough to be certain) that RELAX NG annotations could be
> sufficient to provide a complete mapping from an unchanged XML
> vocabulary to a set of RDF graphs.
Sounds an interesting idea but I have not investigated this area myself.
> In some ways, this feels perverse, as it uses something of a PSVI
> approach to define a mapping between the XML and its RDF reading. At
> the same time, however, RELAX NG patterns feel flexible enough to
> support RDF's many possibilities and to express the different graphs
> which may appear given different co-occurrence constraints. (I'm not
> proposing RELAX NG as a general RDF schema language - I don't think that
> would work. This is _just_ about mapping XML to RDF graphs.)
>
> I don't yet have anything concrete to show, I'm afraid, so this is
> pretty much playing a hunch. Anyone have the same hunch? Anyone have
> reasons why this is obviously impossible? Possible?
>
> [1] - http://www.xml.com/pub/a/2002/10/30/rdf-friendly.html
> [2] - http://www.xml.com/pub/a/2003/08/20/dive.html
Yes, at this point I'd need some examples.
I was wondering if this is a place for PIs similar to how they are used for stylesheets in XML
where the mapping-to-triples schema can be hidden away and still
available to those things that understand it.
<?rdf-mapping href='http://example.org/blah-rdf.rng' type='application/xml'?>
<blah>
...
</blah>
(I was reminded by http://www.w3.org/2001/02pd/rec54 which is an RDF
schema with XSLT->XHTML sheet specified)
Dave
[*] Redland http://www.redland.opensource.ac.uk/
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