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Re: Implementing statement grouping, contexts, quads and scopes (was: Re: Out of context, in context, out of subject ????)

From: Patrick Stickler <patrick.stickler@nokia.com>
Date: Mon, 24 Jun 2002 10:57:58 +0300
To: Patrick Stickler <patrick.stickler@nokia.com>, ext Jonathan Borden <jonathan@openhealth.org>, <areggiori@webweaving.org>, Didier <didier@phpapp.org>
CC: RDF Interest <www-rdf-interest@w3.org>, RDF Logic <www-rdf-logic@w3.org>
Message-ID: <B93CABB6.173D0%patrick.stickler@nokia.com>

On 2002-06-24 10:47, "ext Patrick Stickler" <patrick.stickler@nokia.com>

> On 2002-06-21 15:53, "ext Jonathan Borden" <jonathan@openhealth.org> wrote:
>> The concept of "dark triples" as a layering option seems to be getting a bit
>> misunderstood. The essence of "dark" or "unasserted" triples is simply that,
>> from a technical perspective, it is difficult (some would indeed say
>> impossible) to define a language such as OWL (and given the constraints
>> placed on this language by the WebOnt charter etc.) in RDF if OWL is to have
>> the characteristics we desire, and RDF triples are all "truths".
> I consider RDF to already have a mechanism for expressing unasserted
> triples, namely reification. The only reason folks want to create something
> else, IMO, is simply because the RDF/XML syntax is so obese. I.e.
>  <rdf:Statement>
>     <rdf:subject   rdf:resource="#foo"/>
>     <rdf:predicate rdf:resource="&owl;bar"/>
>     <rdf:object    rdf:resource="#bas"/>
>  </rdf:Statement>
> It seems to me that the solution is simply to add a contracted form
> of reification, to make the existing mechanism more palatable. E.g.
>  <rdf:Statement rdf:about="#foo">
>     <owl:bar rdf:resource="#bas"/>
>  </rdf:Statement>
> Yes, this is a (minor) change to RDF/XML parsing, but IMO a far
> cheaper cost than any of the other proposals on the table for
> signaling "dark" triples. Note that it does not constitute a
> change to the RDF syntax, only to the special interpretation
> of rdf:Statement in contracted rather than full form. I.e it's
> only a change to the RDF/XML parsing algorithm. And since all
> RDF parsers are going to *have* to be revised to support the
> already adopted changes to RDF/XML, this is not a big deal.
> What more does OWL (or any other layer) need? An OWL application is
> then free to treat unasserted RDF statements employing OWL predicates,
> as asserted at the OWL layer, without any impact at all to RDF-only
> applications and without requiring RDF-only applications to know
> anything about any higher layers or (most importantly) needing to
> explicitly know which predicates in otherwise RDF asserted triples
> are "dark" and must actually be treated as unasserted at the
> RDF layer (what nonsense).
> Regards,
> Patrick
> --
> Patrick Stickler              Phone: +358 50 483 9453
> Senior Research Scientist     Fax:   +358 7180 35409
> Nokia Research Center         Email: patrick.stickler@nokia.com

Note also that unasserted "dark" statements at the RDF-level can be
asserted at any given higher level where they have meaning in a automated
and generic fashion.

OWL level assertions can be easily automated using this approach
by a single rule:

   ?x rdf:type rdf:Statement .
   ?x rdf:subject ?s .
   ?x rdf:predicate ?p .
   ?x rdf:object ?o .
   ?p rdf:type owl:OWLPredicate .
   ?s ?p ?o .


This, of course, presumes that all OWL predicates are typed
as owl:OWLPredicate, but that's pretty cheap.

Higher layers built on top of OWL can just inherit OWLs
layer specific assertion rule as above, in addition to
their own.



Patrick Stickler              Phone: +358 50 483 9453
Senior Research Scientist     Fax:   +358 7180 35409
Nokia Research Center         Email: patrick.stickler@nokia.com
Received on Monday, 24 June 2002 03:53:31 UTC

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