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Re: Comments on SPARQL Query Language for RDF (21 July) (OWL inference and query)

From: Dan Connolly <connolly@w3.org>
Date: Tue, 06 Sep 2005 13:44:10 -0500
To: Ora Lassila <ora.lassila@nokia.com>
Cc: Art.Barstow@nokia.com, public-rdf-dawg-comments@w3.org
Message-Id: <1126032250.16011.946.camel@dirk>

On Tue, 2005-09-06 at 11:00 -0400, Ora Lassila wrote:
> Dan et al,
[...]
> > The link was not as clear as it could be in the 2005-07-21 version;
> > In response to comments from other reviewers, we have clarified
> > the references section. In the current editor's draft, you
> > may want to look at...
> >   http://www.w3.org/2001/sw/DataAccess/rq23/#RDF-MT
> 
> I will obviously have to read the most recent version first to see what you
> have done. It does seem, though, that since queries are (potentially) run
> against the deductive closure of a graph, the query language does not extend
> easily to representations which do not have a single unique deductive
> closure (which as far as I understand happens as soon as you have mutually
> exclusive entailments as in OWL).

Our most recent version doesn't address the case of entailments
that don't have a unique deductive closure.

That would be out of the scope of our charter. More below...

[skipping the transitive closure discussion for now...]

> >> 3) It does not seem possible to extend SPARQL to be
> >> used with OWL (primarily, perhaps, because of comment
> >> #1 above).
> > 
> > A number of WG members (UMD, Agfa) are succesfully using SPARQL
> > with OWL.
> > 
> > By charter, OWL inference is orthogonal to query:
> > 
> > [[
> > 2.1 Specification of RDF Schema/OWL semantics
> > 
> > The protocol will allow access to a notional RDF graph. This may in
> > practice be the virtual graph which would follow from some form of
> > inference from a stored graph. This does not affect the data access
> > protocol, but may affect the description of the data access service. For
> > example, if OWL DL semantics are supported by a service, that may be
> > evident in the description of the service or the virtual graph which is
> > queried, but it will not affect the protocol designed under this
> > charter.
> > ]]
> > http://www.w3.org/2003/12/swa/dawg-charter#rdfs-owl-queries
> > 
> 
> I guess I don't really understand how such an approach would work. I can see
> that you could query a graph that *syntactically* represents your OWL but
> not more. The beauty of RDF is that we have a uniquely defined deductive
> closure, but this is not the case for OWL.

Indeed, OWL entailments that don't have a single deductive closure
are not accommodated by the approach in the charter.

>  Of course, the "neats" do not
> like this approach even with RDF, but myself, being a "scruffy", can live
> with it. ;-)

Hmm... now it's even less clear to me what changes, if any, you're
asking for. Help?

> I will have to take a look what exactly the UMD and Agfa folks have done.

I misspoke when I said that UMD was successfully using OWL with SPARQL.

Note clarification from Hendler:

[[
  We have continued to support the design of SPARQL because we do a 
significant amount of work with respect to RDF triplestores and we 
very much want to do distributed triple store linking, but we do not 
consider SPARQL to be very useful for OWL as per Nokia's comments.
]]
 -- http://lists.w3.org/Archives/Public/public-rdf-dawg-comments/2005Sep/0009.html

>     - Ora
> 
-- 
Dan Connolly, W3C http://www.w3.org/People/Connolly/
D3C2 887B 0F92 6005 C541  0875 0F91 96DE 6E52 C29E
Received on Tuesday, 6 September 2005 18:44:21 GMT

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