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Re: Dark triples, current closure / entailment rules, can someone clarify?

From: Jan Grant <Jan.Grant@bristol.ac.uk>
Date: Tue, 25 Jun 2002 11:07:05 +0100 (BST)
To: patrick hayes <phayes@ai.uwf.edu>
cc: w3c-rdfcore-wg@w3.org
Message-ID: <Pine.GSO.4.44.0206251103390.27038-100000@mail.ilrt.bris.ac.uk>

On Mon, 24 Jun 2002, patrick hayes wrote:

>
> >Pat indicated at the F2F that entailments "accidentally" drawn would be
> >"harmless".
>
> RDF entailments, yes.
>
> >Can someone clear up this example for me?
> >
> >A:
> >	<eg:foo1> <rdf:subPropertyOf> <dark:eg:foo2> .
> >	<dark:eg:foo2> <rdf:subProperotyOf> <eg:foo3> .
> >
> >	<eg:a> <eg:foo1> <eg:b> .
> >
> >B:
> >	<eg:foo1> <rdf:subPropertyOf> <dark:eg:foo2> .
> >	<dark:eg:foo2> <rdf:subProperotyOf> <eg:foo3> .
> >
> >	<eg:a> <dark:eg:foo2> <eg:b> .
> >
> >C:
> >	<eg:foo1> <rdf:subPropertyOf> <dark:eg:foo2> .
> >	<dark:eg:foo2> <rdf:subProperotyOf> <eg:foo3> .
> >
> >	<eg:a> <eg:foo3> <eg:b> .
> >
> >
> >Does A |= C? Does A |= B? B |= C?
>
> Yes:
> A|= C (by subproperty chaining and then the subproperty closure rule)
> No:
> A |= B (dark conclusion)

Actually, for the same reason, isn't this a "yes"? Because the non-dark
statements are a strict subset of the antecedent?

> B |= C (dark, ie missing, antecedent)
>
> However, notice that should be rdfs:subPropertyOf. To anticipate your
> next question: yes, one does have to be careful using darkened
> triples in RDFS hierarchical inferences (basically, any kind of
> transitivity implication, ie subPropertyOf and subClassOf.)  What I
> claimed was that it was safe with RDF-valid reasoning (ie
> effectively, existential generalization).

To be honest, I think examples like this are why we should have an
explicit, not implicit name-based, darkening mechanism. At the F2F I was
in favour of it, but the more I think about it the more it seems like a
mistake to key this off property names. Some explicit syntax mechanism
(either Patrick's, or an "rdf:asserted='True'" or such) seems much less
error-prone... particularly if we can provide a little more sugar by
having shorthand constructs (daml:collection) that normally produce some
darkened triples do that "by default".

jan

-- 
jan grant, ILRT, University of Bristol. http://www.ilrt.bris.ac.uk/
Tel +44(0)117 9287088 Fax +44 (0)117 9287112 RFC822 jan.grant@bris.ac.uk
and Nostradamus never dreamed of the Church of the Accellerated Worm
Received on Tuesday, 25 June 2002 06:09:43 EDT

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