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Re: Why? Re: rdf as a base for other languages

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Sat, 02 Jun 2001 17:43:15 -0400
To: seth@robustai.net
Cc: www-rdf-logic@w3.org
Message-Id: <20010602174315B.pfps@research.bell-labs.com>
From: "Seth Russell" <seth@robustai.net>
Subject: Re: Why? Re: rdf as a base for other languages
Date: Sat, 2 Jun 2001 12:45:16 -0700

> From: "Peter F. Patel-Schneider" <pfps@research.bell-labs.com>
> 
> > I'm sorry but I do not see the ability to define and use contexts in RDF
> at
> > all, nor do I see the ability to have an arc (triple) to be the object of
> > another arc, even with reification.  Remember the only thing that RDF says
> > about reified statements (i.e., resources with rdf:type rdf:statement) is
> > that they have exactly one rdf:subject, one rdf:object, and one
> > rdf:predicate.
> 
> Interesting!   I take it you are aware that a triple must be unique (at
> least in an idealistic sense) in that each of it's component parts are
> guaranteed to be unique by virtue of the URI system.  

Yes, triples are unique, according the Formal Model of RDF, in that there
can only be one triple with the same three parts.  Yes, the component parts
of a triple are uniquely determined by the triple.

> And that you are aware
> that we can construct a symbol (which symbol is the riefied statement) that
> stands for exactly one and only one triple, and if that that symbol can be
> an object of a RDF statement.  

This is where I disagree.  The four triples

	<RDF:predicate,r,p>
	<RDF:subject,r,s>
	<RDF:object,r,o>
	<RDF:type,r,RDF:Statement>

don't stand for anything in the Formal Model of RDF, except the four
triples.  Yes, there is wording in the Formal Model of RDF (point 9) that
calls r the reification of the triple <p,s,o>, but there is no impact of
this in the model.  

> Then can you tell me the difference between a
> statement having a reified statement as it[]s object and a statement having
> the statement itself as it's object?   

If a statement is the object, then it is asserted.  If a resource that has
type Statement is the object, then the thing or things that are asserted
are quite different.  Consider the RDF data model resulting from the two
situations.  They are quite different.

> Me thinks you draw a distinction that
> makes no difference.

On the contrary, there is a large difference between pointing to something
that asserts a base fact and pointing to something that does not assert
that base fact.

> Seth Russell

peter
Received on Saturday, 2 June 2001 17:44:51 GMT

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