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Re: RIF/SPARQL Semantics (Was -- Rule usage description...)

From: Axel Polleres <axel.polleres@deri.org>
Date: Sun, 12 Dec 2010 17:21:07 +0000
Cc: "Lee Feigenbaum" <lee@thefigtrees.net>, "Semantic Web" <semantic-web@w3.org>, <public-rdf-dawg-comments@w3.org>
Message-Id: <831F7707-E938-49C9-8335-46B9F686B6BB@deri.org>
To: "Adrian Walker" <adriandwalker@gmail.com>
Hi Adrian,

As for RIF, there is no negation available as such in the RIF Core [1] and RIF BLD [2] dialects
(which doesn't preclude other dialects to define negation, e.g. the RIF PRD [3] dialect has negation), 
but there will be MINUS in SPARQL1.1 Query, see Section 8 of the current working draft [4]. You will 
also find the current state of aggregates there in Section 10 [5].

Hope that helps,

best regards, 
Axel

1. http://www.w3.org/TR/rif-core/
2. http://www.w3.org/TR/rif-bld/
3. http://www.w3.org/TR/rif-prd/
4. http://www.w3.org/TR/sparql11-query/#negation
5. http://www.w3.org/TR/sparql11-query/#aggregates

On 12 Dec 2010, at 17:01, Adrian Walker wrote:

> Hi Lee,
> 
> You wrote...
> 
> The SPARQL Query Language is defined in terms of algebraic semantics, rather than a model theoretic semantics. The original Data Access Working Group did consider this suggestion and decided to remain with the existing approach, in addition to the test suite. The current SPARQL Working Group also intends to publish a test suite to aid interoperability in implementations of SPARQL 1.1.
> 
> Where do things stand currently with the semantics of negation and aggregation please?  (At one time, RIF/SPARQL negation was out of semantic scope, but with several different hacks available -- a sure sign of future trouble if not addressed with a spec)
> 
>                                   Thanks,  -- Adrian
> 
> Internet Business Logic
> A Wiki and SOA Endpoint for Executable Open Vocabulary English Q/A over SQL and RDF
> Online at www.reengineeringllc.com    
> Shared use is free, and there are no advertisements
> 
> Adrian Walker
> Reengineering
> 
> 
> On Sun, Dec 12, 2010 at 10:49 AM, Lee Feigenbaum <lee@thefigtrees.net> wrote:
> On 12/12/2010 9:23 AM, Adrian Walker wrote:
> Hi Ivan & All --
> 
> There would seem to be an opportunity here to move the W3C approach to
> rules and SPARQL onto a firmer semantic base.
> 
> Hi Adrian,
> 
> Please send any comments on the SPARQL 1.1 documents to public-rdf-dawg-comments@w3.org.
> 
> 
> The basic idea is to define what answers a rule system or SPARQL should
> give to /any /question, based on /any /set of triples, using a logical
> model theory.  The theory then works as a "gold standard" for
> implementers.  W3C could provide test suites.
> 
> The SPARQL Query Language is defined in terms of algebraic semantics, rather than a model theoretic semantics. The original Data Access Working Group did consider this suggestion and decided to remain with the existing approach, in addition to the test suite. The current SPARQL Working Group also intends to publish a test suite to aid interoperability in implementations of SPARQL 1.1.
> 
> best,
> Lee
> 
> Looking backwards for a moment, SQL suffers from  the lack of such a
> base or standard.  There is a query which produces different answers
> over the same data in two of the leading  SQL implementations (and both
> answers are intuitively wrong).  That's not fatal for SQL, since one can
> 'program around it', but a similar flaw is extremely serious for
> RIF/SPARQL, since it's supposed to work the same everywhere on the Web.
> How would we ever trust the answers?
> 
> An early version a model theoretic standard is in [1,2].   There's an
> illustration of how it can work in practice with RDF in [3,4].
> 
> Hope this helps.
> 
>                                      -- Adrian
> 
> [1]  Towards a Theory of Declarative Knowledge, (with K. Apt and H.
> Blair). In: Foundations of Deductive Databases and Logic Programming, J.
> Minker (Ed.), Morgan Kaufman 1988.
> http://oai.cwi.nl/oai/asset/10404/10404A.pdf
> 
> [2]  Backchain Iteration: Towards a Practical Inference Method that is
> Simple   Enough to be Proved Terminating, Sound and Complete. Journal of
> Automated Reasoning, 11:1-22
> 
> [3] www.w3.org/2004/12/rules-ws/paper/19
> <http://www.w3.org/2004/12/rules-ws/paper/19>
> 
> 
> [4] www.reengineeringllc.com/demo_agents/RDFQueryLangComparison1.agent
> <http://www.reengineeringllc.com/demo_agents/RDFQueryLangComparison1.agent>
> 
Received on Sunday, 12 December 2010 17:21:40 GMT

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