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RE: Where does RDF fit in with XQuery?

From: Gary Zakon <gzakon@rcn.com>
Date: Fri, 22 Jun 2001 11:44:28 -0400
To: "Libby Miller" <Libby.Miller@bristol.ac.uk>, <www-rdf-interest@w3.org>, <www-ql@w3.org>
Message-ID: <NEBBLAKMIKCEKBEKMHDIOEKICBAA.gzakon@rcn.com>
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?

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?

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:
http://139.91.183.30:9090/RDF/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 Friday, 22 June 2001 11:40:21 GMT

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