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Re: [UCR] ISSUE-12 and ACTION6198 (semantic web rule language) - and also the SPARQL topic

From: Axel Polleres <axel.polleres@urjc.es>
Date: Wed, 10 Jan 2007 09:02:52 +0100
Message-ID: <45A49DAC.6060607@urjc.es>
To: Dave Reynolds <der@hplb.hpl.hp.com>
CC: RIF WG <public-rif-wg@w3.org>

Dave Reynolds wrote:
> Axel Polleres wrote:
>> Just one question, if we
>> a) can show that SPARQL itself maps to a RIF dialect (which allows to 
>> access RDF and OWL data) and calls of built-in functions like CXpath 
>> functions etc. and
>> b) view SPARQLs CONSTRUCT queries as well as nothing else than a rule 
>> dialect (at least the expressivity of SWRL, i.e. HORN over RDF/OWL 
>> atoms is for sure covered with such construct queries)
>> then we solve both issues: the one of a semantic Web rules language
>> (just using SPARQL CONSTRUCT as its syntax and interchange with other 
>> rules on top of RDF enabled via its RIF version)
> Sorry, I don't quite understand that.
> First, SPARQL query was just an example of what you might want in a 
> semantic web rule language.

What I meant to say is: SPARQL's CONSTRUCT, has already quite a lot 
(probably not all, but it is a start) what a rules language on top of 
OWL/RDF would need, and for many users, this might be sufficient as a 
starting point for writing SW rules.

> Second, this discussion was about whether all RIF dialects are 
> automatically semantic web rule languages and the fact that the working 
> group doesn't want to endorse a specific semantic web dialect. 

In this sense, I might have left the topic a bit... but my worry was 
that: At least for most uses I can imagine for a rules language on top 
of RDF/OWL, ie. what I understand as a useful starting point for an SW 
rules language, SPARQL CONSTRUCT statements, read as rules, seem to be 
more than enough syntaxwise. Alignment with RIF dialects, or at least 
the definition of which RIF dialect this corresponds to would thus be 
desirable IMO.

> You seem 
> to be proposing a specific dialect.

Not at all, What I say is that if we clearly define a dialect 
corresponding to SPARQL what more or less is expressible by CONSTRUCT 
statemants (if we allow RDF triples being inferred in the rule head and 
SPARQL queries in the rule body, this is more or less what we get 
anyway), then we even have a starting point for an agreed syntax of a 
semantic web rules language already. I don't say that it is a task of 
RIF to further elaborate or extend this in the future, but it
a) would be a nice joint work with the DAWG to go for such a joint 
solution towards a lighteight SW rules language on top of SPARQL.
b) would fulfill the requirement to provide the foundations for dialects 
to use as an SW rules language IMO.

>> and the one how to integrate SPARQL queries in conditions semantically 
>> (one could still view it as a blackbox as well, of course, but SPARQL 
>> queries would be equally definable as part of an extended rule set.)
>> I have made an attempt on this which I also posted to this list some 
>> time before Christmas, see :
>> http://lists.w3.org/Archives/Public/public-rif-wg/2006Dec/0002 
> It has been suggested to me that there are differences between the 
> semantics of SPARQL assumed there and what's in the current spec but I'm 
> afraid I haven't studied the proposal enough myself yet to properly 
> comment on the details.

I called it an attempt before, and since the formal algebra of SPARQL 
appeared to me at the time of writing a still "moving target" I decided 
to stick with the semantics defined by Perez et al at ISWC'06 rather 
than on the spec. I am convinced that small deviations can be 
reconciled, but I am waitng for the finalization of SPARQL's algebra to 
do this and see how/whether there will be still changes there.

What I am proposing is simply to collaborate on the topic of a SW rules 
language with the DAWG, since this seems to me at the moment the most 
promising path to get some viable suggestion for a people to write down 
  RDF rules without the need to introduce another new syntax for it. My 
idea was more that e.g. the two WGs could produce a joint document in 
this sense as a "by product" as none of the two claims to be chartered 
towards standardizing "the" SW rules language, but users still need a 
way to write them down.

My fear of course is that neither of both groups really has resources 
for such work, but if anybody would volunteer to jump in and go for 
something like that, and also other people agree that this could be a 
starting point, I'd be happy to attempt to reactivate the vacant 
"liaison" with DAWG and work further in that direction (although 
probably an official "liaison"is only possible through members of the DAWG?)


Dr. Axel Polleres
email: axel@polleres.net  url: http://www.polleres.net/
Received on Wednesday, 10 January 2007 08:03:17 UTC

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