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Re: [TF-ENT] RDFS entailment regime proposal

From: Chimezie Ogbuji <ogbujic@ccf.org>
Date: Tue, 29 Sep 2009 10:52:51 -0400
To: "Birte Glimm" <birte.glimm@comlab.ox.ac.uk>
cc: "SPARQL Working Group" <public-rdf-dawg@w3.org>
Message-ID: <C6E79783.CBD4%ogbujic@ccf.org>
On 9/28/09 7:28 AM, "Birte Glimm" <birte.glimm@comlab.ox.ac.uk> wrote:
>>> [..] 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.

> Hm, I don't think I get your point here. The sentence you cite is just
> an explanation of why we do only provide an RDFS entailment regime and
> not also an RDF entailment regime. Should I rephrase that?

Oh, I see.  I mist that context.

>>> .. 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?
 
> under the restriction that I propose you would get { ?x-><ex:c> } and
> that is it. None of the blank nodes occured in the input, so they can
> be used in the derivation of consequences, but they will now show up
> in answers. I that ok to you or do you have an alternative proposal?

That's ok to me.

>> 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.

> ASK { rdf:_1 rdf:type rdf:property }
> against the empty graph, I would get true since this is an axiomatic
> triple and rdf:_1 occurs in the signature of the query.
 
Right., but the answers here come with a caveat (i.e., they were under an
entailment regime with possibly unsafe queries)

> If I then go on to ask
> SELECT ?x WHERE { ?x rdf:type rdf:property }
> again against the empty graph, I get an empty answer set. That is not
> what I expect. I just learned that the triple rdf:_1 rdf:type
> rdf:property is entailed (ASK query), but then I get no answer when I
> replace rdf:_1 with a variable. That is what happens under the current
> definition and that is not nice.

Yes, on some level it is definitely not nice.  I just wonder how liable can
the system be given the caveat that already comes with the previous answer.

-- Chimezie


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Received on Tuesday, 29 September 2009 15:05:21 GMT

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