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RE: A triple is not unique.

From: Jonathan Borden <jborden@mediaone.net>
Date: Sun, 19 Nov 2000 17:04:08 -0500
To: "McBride, Brian" <bwm@hplb.hpl.hp.com>
Cc: "Seth Russell" <seth@robustai.net>, "RDF-IG" <www-rdf-interest@w3.org>
Message-ID: <000001c05274$a4177aa0$0201a8c0@ne.mediaone.net>
McBride, Brian wrote:

> For the record, section 5, the formal model section of M&S states:
>   There is a set called Statements, each element of which is a triple
>   of the form {pred, sub, obj}
> That says that each Statement is a triple of the form (s,p,o).  A
> triple in mathematics is uniquely determined by its three components.

Thank you, thank you, thank you, thank you. This statement is not ambiguous.
Also note that a "set" of triples as opposed to what is sometimes called a
"multiset" may have at most one of a unique (p,s,o).

> >
> > My vote is on allowing identical statements with diffrent identities.
> >
> Can you clarify what that sentence means :)  How can two identical things
> have different identity?  If they  have different identity, they are not
> identical!

I think he means that he would like to assign different IDs in the SGML/XML
sense to a statement, which would affect the reified statement, i.e.
(asserts, Hugo, X) and (asserts, Frodo, X') but unfortunately (or
fortunately :-)) this just isn't part of the RDF Model.

> > And you can't avoid that with statements distributed over several
> > models over the net.

Aha, yes this is a practical problem, i.e. within several 'documents' on the
net an identical triple may be asserted. This gets back to the 'context'
discussion. Prior systems have included the concept of a 'space' which
provides a name to a set of statements, effectively requiring each statement
to be a quad:

 (p,s,o, space/context).

Alternatively, we might consider the URI of the subject prior to the
fragment identifier (otherwise known as the namespace URI). In any case I
think it is sometimes useful to consider a (sub)set of statements together,
and in this context (sic :-) it is useful to give a name to individual
subsets of statements.

Jonathan Borden
The Open Healthcare Group
Received on Sunday, 19 November 2000 16:58:35 UTC

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