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Re: [TF-ENT] RDFS entailment regime proposal

From: Chimezie Ogbuji <ogbujic@ccf.org>
Date: Sat, 26 Sep 2009 01:48:19 -0400
To: "Birte Glimm" <birte.glimm@comlab.ox.ac.uk>, "SPARQL Working Group" <public-rdf-dawg@w3.org>
Message-ID: <C6E32363.CAAB%ogbujic@ccf.org>
On 9/24/09 1:30 PM, "Birte Glimm" <birte.glimm@comlab.ox.ac.uk> wrote:
> whoever is interested in RDFS entailment: I would be very happy about
> comments and suggestions for the RDFS entailment regime as outlined
> in:
> http://wiki.webont.org/page/SPARQL/OWL

Hey Birte.  I have a few comments, focusing mostly on the technical content
rather than style, wording, etc.

> [..] The only additional answers from RDFS compared to RDF are some axiomatic
triples, plus any IRI used as a property will end up as part of an answer to ?p
rdf:type rdf:Property.

The initial language here seems to suggest ruling out answers that, when
substituted into the pattern instance, result in graphs which can be derived
from SG, axiomatic triples, and the application of the RDFS entailment
rules.  Later on, however, the RDFS entailment relation is used in defining
the solution mappings for the query answers.

> There are a view design choices that I have listed at the end of the
> section on RDFS, which could be an alternative to the currently
> proposed way of restricting the answers sets to a finite size. Please
> let me know prefer any of them or have any other suggestions.

> .. if μ(v) is a blank node, then μ(v) occurs in the scoping graph SG

So, is the general intuition here that answers where subject terms are Blank
nodes must "refer" to a priori blank nodes in the SG?

> Ideally,
> a monotonic behavior for queries would be very nice, but that is not
> easy to achieve when solution sequences are possibly infinite without
> restrictions.

Well, isn't monotonic usually a characteristic of an entailment
relationship? In this case it is not the RDFS entailment relationship that
is monotonic (in the sense of the word I'm used to, anyways), but rather
there is a difference in answers based on whether or not pattern
substitutions involve terms in some combination of either the signature of
the SG or the query.

But, how does

ASK { rdf:_1 rdf:type rdf:property }

provide an answer via the entailment regime if the possible solutions for a
BGP under an entailment relationship is defined only WRT the variables in
the query but there are none in this query?

I like the 2nd option amongst the alternative design choices. It requires
that if the user makes the mistake of giving a query that would normally
give infinite answers (the use of patterns that match against axiomatic
triples being one example), they must provide a restriction on the solution
set.  Having no control over the returned answer seems reasonable given the
'unsafe' nature of the query.

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


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Received on Saturday, 26 September 2009 05:50:12 GMT

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