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Re: Predicates and Arcs vs Triples RE: use/mention and reification: rdf:predicate/subject/object

From: Graham Klyne <GK@ninebynine.org>
Date: Fri, 01 Jun 2001 16:39:00 +0100
Message-Id: <>
To: "Geoff Chappell" <geoff@sover.net>
Cc: "Jonathan Borden" <jborden@mediaone.net>, "pat hayes" <phayes@ai.uwf.edu>, <www-rdf-logic@w3.org>

In broad terms I agree with the sentiments you express.  But there are some 
specific issues that call for investigation:

(a) being able to express things like (?a ?b ?c) and (says John (?a ?b ?c)) 
seem to be things that the core RDF should be able to do in a logically 
clean, consistent and simple fashion.

(b) I would like to see an RDF core that can be interpreted consistently by 
processors that implement different higher-level semantics;  this means the 
core must be well-defined, and it must be possible to add new semantics 
(possibly with additional syntax productions) in a way that doesn't rip up 
the core semantics.  (c.f. my comments at the end of [1].)


[1] http://lists.w3.org/Archives/Public/www-rdf-logic/2001May/0388.html

At 09:33 PM 5/31/01 +1000, Geoff Chappell wrote:
> > The model _does not_ contain a mechanism to unreify the statement _as a
> > statement_ i.e. still does not contain the statement:
>Isn't that because rdf is just the first step/layer? RDF has no mechanisms
>to handle variables, quantification, implications, etc. (and so as a
>knowledge representation language it's not particulary expressive.) But
>wasn't that always the plan? My understanding of the rdf roadmap is that RDF
>will serve as a triple-based data model for storage of facts -- with
>reification just a convention to store "preparsed metafacts" that will only
>be given meaning by a processor/logic system higher up in the chain (i.e.a
>system might have a rule:  infer {?a ?b ?c} from {say john {?a ?b ?c}}). So
>much of the argument/confusion about reification seems to stem from the fact
>that it's pretty useless without another layer (and the fact that it tries
>to do too much/has overloaded meaning - with bags, etc.).
>Do others see it differently? is rdf trying to become a fully expressive
>knowledge representation language -- a la kif -- in and of itself ?  There
>seems to be so much blurring at times between the rdf triple model, its xml
>serialization, and the logic layer(s) that act upon it. I worry that if
>those layers aren't kept distinct (at least conceptually) poor decisions
>will be made about where functionality belongs.
>Geoff Chappell

Graham Klyne
Received on Friday, 1 June 2001 11:42:07 UTC

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