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Re: Where does RDF fit in with XQuery?

From: Libby Miller <Libby.Miller@bristol.ac.uk>
Date: Wed, 27 Jun 2001 13:24:22 +0100 (BST)
To: gzakon@rcn.com, d.m.steer@lse.ac.uk
cc: www-rdf-interest <www-rdf-interest@w3.org>, www-ql <www-ql@w3.org>
Message-ID: <Pine.GSO.4.21.0106271312030.24485-100000@mail.ilrt.bris.ac.uk>

Hi Gary

> Libby,
> Thank you - this does help.  I do understand why you would want to query RDF
> using an RDF oriented query language vs. XQuery.  However, I still have a
> question that perhaps I can formulate better now:
> If RDF provides meta-information regarding the relationship between two
> different XML document types can I use this meta-information to help me
> formulate an XQuery that extracts information from the two related document
> types?  In other words, do I use RDF to assert relationships between XML
> document types that cannot be asserted using XML Schema?  My understanding
> is that XML Schema provides the meta-information for a single XML document
> type and cannot provide meta-information describing the relationship between
> XML document types.  RDF is for this purpose, correct?

This is an interesting idea. I've been pondering it over a few days
with a friend of mine, Damian Steer, who isn't on these lists. He
suggested that you might be able to use RDF to point into XML schema
documents and say things like thisTag is equivalent to
thisOtherTag. You could point into XML schemas in RDF using Xpointer (as
I know EARL are doing for XML instance documents). RDF schema itself
doesn't enable you to say that classes are equivalent, but the DAML work
extends RDF to be able to do this.
So what this would mean is that we might be able to query several
XML instance documents with different XML schemas by using information
that could be encoded in RDF. I don't really know enough about Xquery
to know what this would look like though.
So there are two possible routes for achieving mapping between XML
schemas (and probably more): RDF/DAML or XSLT. They seem to have some
overlap in application. The former is more 'meaningful' (it has to do
with the semantics of the schemas), whereas the latter is purely
mechanical. The former looks like it could be a better solution in this

> Does RDF meta-information ever include instance data from the XML documents
> being described?  Which use is more prevalent - providing meta-information
> regarding XML document types or providing meta-information regarding XML
> document instances?  Does this question make sense?

RDF meta information could include XML using the seldom-implemented
parse type=Literal syntax. If so, the RDF processor would ignore this.
One common use of RDF is describing web pages (instances). I don't know
any when use RDF to describe XML documents (schemas or instances) unless
you count Xhtml. There is EARL, which describes parts of Xhtml or XML
document instances using RDF.

Your questions make sense...hope this helps


EARL: http://www.w3.org/2001/03/earl/
DAML: http://www.daml.org/2001/03/daml+oil-index

> Thanks again,
> Gary
> -----Original Message-----
> From: www-ql-request@w3.org [mailto:www-ql-request@w3.org]On Behalf Of
> Libby Miller
> Sent: Thursday, June 21, 2001 9:21 PM
> To: Gary Zakon
> Cc: www-ql; christop@ics.forth.gr
> Subject: Re: Where does RDF fit in with XQuery?
> hi Gary
> I think there are a few people working on the relationship between
> Xquery and RDf query languages at the moment, among them Jonathan Robie
> (XQuery) and Vassilis Christophides and others (RQL). I've been helping
> Jonathan out with the RDF side of things.
> Basically, because there are many different ways of serializing any
> given RDF description of, say, a document in XML (see examples in the
> RDF model and syntax - http://www.w3.org/TR/REC-rdf-syntax/), XQuery
> isn't the easiest way to query RDF. A more straightforward way is to
> query the underlying model, which is based on triples, regardless of the
> exact syntax. This is what I've done with my prototype RDF query
> language Squish, and what the RQL people have done in a rather more
> finished way.
> So it would be nice to query xml documents and the meta-information
> about them in one format, but this looks difficult unless the RDF is in
> some canonical format (there isn't one for RDF at least at the moment).
> As regards schemas, I would think that XMLSchema would be more useful
> for guidence on the sort of XQueries against XML documents that are
> likely to be sucessful. RDF Schemas can perhaps help you with RDF
> queries.
> does that help at all?
> RQL:
> Squish:
> http://swordfish.rdfweb.org/rdfquery/
> RQL/Squish comparison demo
> http://swordfish.rdfweb.org/discovery/2001/06/squishtests/
> Libby
> On Thu, 21 Jun 2001, Gary Zakon wrote:
> > Hi,
> >
> > I'm struggling a bit with understanding the role of RDF and its
> relationship
> > to XML Schema and now XQuery.  Any help anyone can offer to clarify things
> a
> > bit is much appreciated.
> >
> > What role (if any) does RDF play with respect to XQuery?  XQuery allows me
> > to query across multiple XML documents.  If those documents are described
> > using RDF does that help me formulate my queries in any way?  For example,
> > RDF can inform me of the relationships between different XML documents.
> Or
> > is the XML Schema for those documents more relevant?  Or are they both
> > relevant?
> >
> > Thanks,
> >
> > Gary
> >
> >
Received on Wednesday, 27 June 2001 08:25:47 UTC

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