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

From: Geoff Chappell <geoff@sover.net>
Date: Thu, 31 May 2001 21:33:07 +1000
Message-ID: <00b101c0e9c5$7726e240$0400a8c0@GSC866>
To: "Jonathan Borden" <jborden@mediaone.net>, "pat hayes" <phayes@ai.uwf.edu>, "Graham Klyne" <GK@NineByNine.org>
Cc: <www-rdf-logic@w3.org>

----- Original Message -----
From: "Jonathan Borden" <jborden@mediaone.net>
To: "pat hayes" <phayes@ai.uwf.edu>; "Graham Klyne" <GK@NineByNine.org>
Cc: <www-rdf-logic@w3.org>
Sent: Friday, June 01, 2001 10:30 PM
Subject: Re: Predicates and Arcs vs Triples RE: use/mention and reification:
rdf:predicate/subject/object


>
> Jonathan Borden
> The Open Healthcare Group
> http://www.openhealth.org
>
> ----- Original Message -----
> Graham Klyne wrote:
>
> > I'll hazard an opinion that what you describe as genuine reification is
> > handled in RDF by literals, without any built-in interpretation.  Thus,
to
> > distinguish between:
> >
> >     John says "The sky is blue"
> > and
> >     John says-that (the sky is blue)
> >
> > I think RDF aims to handle the latter, but not the former.  In the
latter
> > case, I think it is an RDF expression associated with John's utterance
> that
> > can be interpreted, not the utterance itself.  The utterance must be
> > expressed (interpreted?) as RDF before it can be "understood" by an RDF
> > processor.
> >
>
...
> Now suppose I enter a statement to the effect that "everything John says
is
> true".
>
> 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
Received on Friday, 1 June 2001 10:52:16 GMT

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