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Re: summary of 'a triple is not unique' and 'statements/reified' statements

From: Seth Russell <seth@robustai.net>
Date: Tue, 28 Nov 2000 11:41:21 -0800
Message-ID: <3A240A61.3A65268B@robustai.net>
To: Libby Miller <Libby.Miller@bristol.ac.uk>
CC: www-rdf-interest@w3c.org
Libby Miller wrote:

> I've been following the threads about statements with interest, and I've
> had a go at summarising them. There's a document at
> http://ilrt.org/discovery/2000/11/statements/

Thanks for your summary. I think it will be a very useful tool to help us
arrive at a consensus on these issues.  If you are considering updating it,
maybe you could add a table of contents with anchors into the document, so
that we might have URIs with with to refer to our various arguments.

Several places you refer to the idea that something or other is either in
"the model" or not;  yet I can find no reference in the literature where
that notion is defined.  Pending a more authoritative definition I would
like to propose my own:

topic: in a RDF data model
definition:  "A notion is [in a RDF data model] iff we can find a triple for
it in that model, or imply a triple for it in that model."
Graphically:  "A notion is [in a RDF data model] iff we can find (or imply)
a particular labeled directed arc for it in the graph."

If this definition flies, then we can evaluate the question of whether
Sergey's technique of using the statement id in the subject slot to reify a
statement is in his RDF data model.

[id1, subject1, property1, object1]

[id2, id1, rdf:type, statement]
[id3, id1, property2, object2]

My claim is that it is not.  True, the node with the subject id1 is the
reification of id1, but we can find no labeled arc for that fact in his
model.  Rather we need to call upon notions about an erstwhile 1-to-1
correspondence between reified statements and their referents.

Whereas if we reify statements by putting the id in the object slot, both
the reified statement itself ~and~ the notion that it reifies is in that
model:

[id4, s2, rdf:type, statement]
[id5, s2, reifies , id1]
[id6, s2, property2, object2]

This technique allows us to "hang" exactly what we mean by reification off
of the property [reifies] .. even perhaps to put it in a schema.

Now it can be argued that id2 is in fact the arc I seek, and that off of the
resource [statement] we would hang our notions of reification.  Well we
could do it that way.  Were that the consensus of the group,  i would have
no trouble falling into step.  I am working on some diagrams portraying
reification and context and they can be drawn either way.  I am anxious for
a resolution of the issue so I may show my mentography :))

In defense of Sergey's proposal, I would like to withdraw my allegation that
it would necessarily be less efficient for expressing context information.
As the examples below show, either method could be equally as efficient.

My method:
[id7, context1, asserts, t1]

Sergey's method:
[id8,t1, istin, context1]

Where "istin" is very similar to the CycL "ist" which means "is true in",
and "asserts" is almost as defined by Grahm's "rdfc:asserts".

Mya copa ... mya copa ...

Thanks again for your timely summary!
Seth Russell
Received on Tuesday, 28 November 2000 14:39:12 GMT

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