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Re: my notes on our group discussion today on RDF Query via XQuery, in WWW-2003 BOF on RDF Query&Rules

From: Eric Prud'hommeaux <eric@w3.org>
Date: Sat, 24 May 2003 11:35:42 -0400
To: Patrick.Stickler@nokia.com
Cc: massimo@w3.org, bgrosof@MIT.EDU, www-rdf-rules@w3.org, connolly@w3.org
Message-ID: <20030524153541.GA1579@w3.org>

On Fri, May 23, 2003 at 10:30:25AM +0300, Patrick.Stickler@nokia.com wrote:
> 
> 
> Are we talking here about using a variant of XQuery on RDF/XML
> or on the RDF graph?

We will be updating all RDF graphs. Also, working on transforming
RFC822 messages so we can use SQL to search mail.

But seriously, fear not. XQuery is defined in terms of a data
model. Liam's demo involved re-serializing the RDF but the serious
proposal it to define a mapping between the RDF data model and the
XQuery data model. Since XQuery is both functional and turing
complete, it should be possible to parse RDFXML into some mapped
XQuery data model. However, it is likely that this code would be
handled at a lower level. There is a strong precedent for this in the
form of code shims that expose relational data and other sources as
XQuery data models.

> I personally think it is a big mistake (and this may be stating
> the obvious) to base any RDF query language on any particular
> serialization of the graphl. The RDF MT applies only to the
> graph, and the motivations for various serializations vary
> yet are unified by how they all express the same graph model.
> 
> I'm all for having a recognizable variant of XQuery which is 
> optimized for queries executed against an RDF graph, as that
> can simplify both training and implementation.
> 
> But please, let's not concern ourselves with RDF serializations.
> 
> Cheers,
> 
> Patrick
> 
> 
> > -----Original Message-----
> > From: ext Massimo Marchiori [mailto:massimo@w3.org]
> > Sent: 22 May, 2003 18:07
> > To: Benjamin Grosof; www-rdf-rules@w3.org; eric@w3.org; 
> > connolly@w3.org
> > Subject: RE: my notes on our group discussion today on RDF Query via
> > XQuery, in WWW-2003 BOF on RDF Query&Rules
> > 
> > 
> > 
> > Kudos for having such a BOF, I'm personally happy as it's 
> > touching a subject I've been 
> > pushing on for years... (personal bias admitted ;)
> > In fact, the original plan, now almost lost and buried in 
> > time, was to have RDF-Query based as far as possible
> > on XQuery. I think this requirement still makes lot of sense 
> > (note the "as far as possible").
> > I agree with all what is in these notes. I would particularly 
> > encourage people to 
> > look at where the crucial differences could be: 
> > a) what are the things you can't do with XQuery (using some 
> > serialization): study of use cases. 
> > Possible application of the 80/20 cut.
> > b) secondly, the serialization problem: the power of XQuery 
> > for RDF works much better with some
> > particular serializations other than others. This is a very 
> > interesting subject, and could
> > motivate some normative work on alternative syntaxes for RDF.
> > c) development of extensions to XQuery to get extra power for RDF
> > 
> > There are other issues but these three as the most prominent 
> > three, imho. This would have the strategical
> > consequence of trying a reunion between the 
> > "industrial-strength database side" and the 
> > "semantic-web-rdfish side", which have been kinda disjoint so far.
> > 
> > -M
> > 
> > > -----Original Message-----
> > > From: www-rdf-rules-request@w3.org
> > > [mailto:www-rdf-rules-request@w3.org]On Behalf Of Benjamin Grosof
> > > Sent: Thursday, May 22, 2003 2:21 PM
> > > To: www-rdf-rules@w3.org; eric@w3.org; connolly@w3.org
> > > Subject: my notes on our group discussion today on RDF 
> > Query via XQuery,
> > > in WWW-2003 BOF on RDF Query&Rules
> > > 
> > > 
> > > 
> > > % notes from WWW-2003 BOF discussion on relating RDF-Query to XQuery
> > > % by Benjamin Grosof 5/22/03
> > > 
> > > Here are the notes I took.  Not "official", please post 
> > > corrections/additions to the www-rdf-rules list.
> > > 
> > > Benj, EricP, Andy Seaborne, DanC, general consensus:  worth 
> > looking at
> > > how to do RDF-Q stuff in XQuery:
> > > 
> > > EricP:  XQuery has lots of nice stuff
> > > 
> > > Benj and various: can reduce lots of RDF-Q stuff to XQuery, 
> > front end XQuery
> > > engines with more RDF-specific query lang and then do some
> > > query/result reformulation (incl. later for optimization); even keep
> > > track of; graph vs. tree will matter sometimes; can infer 
> > in rule-ish
> > > manner using ability to return / be constructive in head of query
> > > 
> > > Nick Gibbons:  RDF has aspects of model-theoretic semantics 
> > we need to support
> > > Brian McBride:  probably OK usually to ignore whether stuff 
> > is ground or not
> > > DanC:  want to do some inference about what's true
> > > 
> > > Me:  e.g., use rules for RDFS stuff (e.g., subclassof)
> > > 
> > > TimBL:  there's a FLOWER pattern (Forall Let Where) in 
> > XQuery queries
> > > which is often unnecessarily complex for RDF querying, and 
> > probably hurts
> > > ability to optimize getting at triple stores
> > > 
> > > Andy Seaborne: want to replace the XPath part of XQuery by something
> > > more RDF-specific; good to leverage on XQuery aspects that support
> > > things like XML-Schemas
> > > 
> > > DanC:  want to have test cases that show what XQuery can't do that
> > > we need for RDF-Q
> > > 
> > > EricP and TimBL:  let's have and RDF-Path for simpler stuff, then
> > > another RDF thing
> > > 
> > > TimBL:  let's also look at having a canonical XML syntax for RDF,
> > > lots of people want that
> > > 
> > > Benj:  in TimBL's keynote story about lots of XML data 
> > being put into
> > > RDF to be shared, the expressiveness needed will probably not be
> > > more, or much more, than XQuery supports, so we could get a lot of
> > > leverage from the above; then for stuff that starts out in life as
> > > RDF, we do things using other more RDF-powerful query lang/engines
> > > 
> > > TimBL:  interesting to keep track of what started out as 
> > RDF vs. as XML
> > > 
> > > 
> > > ff-up meeting:  Fri eve
> > > - see by Fri noon:  look on message point, EricP
> > > 
> > > also see WIKI (shared webspace):
> > > http://esw.w3.org/topic/
> > > 
> > > 
> > > 
> > > 
> > ______________________________________________________________
> > __________________________________
> > > Prof. Benjamin Grosof
> > > Web Technologies for E-Commerce, Business Policies, 
> > E-Contracting, Rules, 
> > > XML, Agents, Semantic Web Services
> > > MIT Sloan School of Management, Information Technology group
> > > http://ebusiness.mit.edu/bgrosof or http://www.mit.edu/~bgrosof
> > > 
> > 
> > 

-- 
-eric

office: +1.617.258.5741 NE43-344, MIT, Cambridge, MA 02144 USA
cell:   +1.857.222.5741

(eric@w3.org)
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Received on Saturday, 24 May 2003 11:35:49 GMT

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