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Re: Properties not predicates (was Re: PRIMER: draft data model section)

From: Frank Manola <fmanola@mitre.org>
Date: Wed, 24 Oct 2001 13:52:24 -0400
Message-ID: <3BD6FFD8.37ECBB0@mitre.org>
To: Brian McBride <bwm@hplb.hpl.hp.com>
CC: Pat Hayes <phayes@ai.uwf.edu>, w3c-rdfcore-wg@w3.org

It's not clear to me what distinguishing "statement" and "triple"
accomplishes in this context.  Are we doing "uses" and "mentions"
again?  The M&S (Section 5) says:

"(P162) There is a set called Statements, each element of which is a
triple of the form 
 (P163) {pred, sub, obj}"

I naturally read that as saying that the triples were statements as far
as RDF was concerned (if they weren't, why wasn't the set called
"Triples" instead of "Statements"?).  Morever:

"(P179) From the standpoint of an RDF processor, facts (that is,
statements) are triples that are members of Statements."

I'd agree that the M&S is not a canonical example of precise language,
but as long as we're talking about what the M&S says (or seems to say!),
it seems to say to me that triples are statements.  

Regarding the graph representation:

"(P165) We can view a set of statements (members of Statements) as a
directed labeled graph: each resource and literal is a vertex; a triple
{p, s, o} is an arc from s to o, labeled by p. " 

This says a triple is an arc in the graph.  So if a triple is a
statement (by my reading), then an arc is a statement.  Maybe some more
elaboration would help.  When you say:

> If I write:
> > 
> >    <:sky> <:is> <:blue> .
> >    <:sky> <:is> <:blue> .
> > 
> > I clearly have two triples. 

Do you?  Or do you have two lines of structured text that represent the
same triple?  The same problem exists with "tuples".  You said:

> >    o a statement is an abstraction; its a tuple with three components, subject,

If distinct tuples are identified by three distinct components, then
however many times I write the same three components down, I've still
stated only one tuple.  Is a triple identified only by its components,
or by something else too?  If I say "Frank is confused" 500 times, have
I made 500 (true) statements, or only one?


Brian McBride wrote:
> Pat Hayes wrote:
> >> Just checking we are clear what is being renamed.
> >
> >
> > Well, I thought I was clear, but now I am completely confused.
> >
> >>  M&S uses the term predicate for a component of a statement.
> >
> >
> > That means a triple, right? Or a [node/edge/node] combination in an RDF
> > graph. Or does 'statement' mean something else? Right now, as I
> > understand it, there are triples in Ntriples,  pieces of graph in the
> > graph syntax, and more complicated pieces of syntax in RDF/XML. Which of
> > these is called a statement?
> You have put your finger on a key question, that I think we need to get clear if
>   we are to reconcile the language of the old M&S with the new model theory.
> We are dealing here with two formal models.  M&S has a formal model, and we have
> the new model theory.  I think that M&S has the concept of statement and the new
> model theory does not.
> My *personal* reading of M&S is that statement and triple meant two different
> things.
>    o a statement is an abstraction; its a tuple with three components, subject,
> ...
>    o a triple is a concrete representation of a statement, e.g. state in a
> computer memory, markings on paper etc.
> [I'm not defending this model; I'm just trying to express it.  It may well be
> full of contradictions]
> How do these concepts relate to the new model theory.  Well, a triple in
> n-triples is pretty clearly still a triple.  What is an arc in a graph?  Not a
> statement, I think.  If I write:
>    <:sky> <:is> <:blue> .
>    <:sky> <:is> <:blue> .
> I clearly have two triples.  I would also have two arcs in one of your graphs
> (until it got tidied).  But to M&S, (as I interpret it, others would disagree)
> there is only one statement, because both triples denote the same statement.
> I find no concept similar to statement in the new model theory.
> Brian

Frank Manola                   The MITRE Corporation
202 Burlington Road, MS A345   Bedford, MA 01730-1420
mailto:fmanola@mitre.org       voice: 781-271-8147   FAX: 781-271-8752
Received on Wednesday, 24 October 2001 13:57:11 UTC

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