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Re: "OWL" Entailment

From: Chimezie Ogbuji <ogbujic@ccf.org>
Date: Thu, 07 May 2009 10:12:29 -0400
To: "Bijan Parsia" <bparsia@cs.man.ac.uk>, "SPARQL Working Group" <public-rdf-dawg@w3.org>
Message-ID: <C628648D.A688%ogbujic@ccf.org>
On 5/6/09 1:14 PM, "Bijan Parsia" <bparsia@cs.man.ac.uk> wrote:
> There are some questions that pretty much all more or less expressive
> entailment regimes have to answer to be a sane SPARQL entailment regime:
> 
> 1) If you entail BNodes, what/how many BNodes do you return?
> Example (Simple Entailment):
> s p o entails  s p _:g.
> Should SELECT ?X WHERE {s p ?X} return both s and _:g? (No!)

Agreed.
 
> Compare with:
> s p o.
> s p _:g.
> Where we do *now* get 2 answers (and should).

Agreed.
 
> Example (OWL):
> s rdf:type [a owl:Restriction;
> owl:onProperty :p;
> owl:someValuesFrom owl:Thing]
> entails s p _:g.
> 
> Should SELECT ?X WHERE {s p ?X} return anything? (I say no)

Hmm.. This is tricky.  Can you elaborate on why you think there shouldn't be
any answers here.  I understand that the same argument for the first example
(simple entailment) would apply here, but intuitively it seems to me that a
user-specified existential restriction in this case is more 'suggestive'
(for lack of a better word - I really don't have any principled reason other
than intuition regarding the OWL author's intent) of the s p _:g entailment.

For example, consider:

Brain rdfs:subClassOf [
  a owl:Restriction;
  owl:onProperty part_of;
  owl:someValuesFrom CentralNervousSystem
]

MyBrain a Brain

If the query,

SELECT ?ANATOMY { MyBrain part_of ?ANATOMY }

Returns nothing (as I understand your suggestion above would sanction), a
user might interpret this as suggesting that 'my brain' is not part of
anything even though the OWL axioms say it is necessarily part of the
central nervous system.

> 2) If your data is contradictory, what should you return?
> Typically, contractions entail everything, thus infinite answers.
> Obvious solution is to return a fault (with no answers) and suggest
> using a weaker entailment regime.

Agreed.
 
-- 
----------------------
Chimezie (chee-meh) Thomas-Ogbuji (oh-bu-gee)
Heart and Vascular Institute (Clinical Investigations)
Cleveland Clinic (ogbujic@ccf.org)
Ph.D. Student Case Western Reserve University
(chimezie.thomas-ogbuji@case.edu)


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Received on Thursday, 7 May 2009 14:13:24 GMT

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