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

From: Frank Manola <fmanola@mitre.org>
Date: Thu, 25 Oct 2001 11:29:24 -0400
Message-ID: <3BD82FD4.5000005@mitre.org>
To: Pat Hayes <phayes@ai.uwf.edu>
CC: w3c-rdfcore-wg@w3.org
Pat Hayes wrote:

>> Brian McBride wrote:
>> snip
>>>  This sort of discussion can rathole deep and long.  I've seen it 
>>> many times
>>>  before on rdf interest and elsewhere and never get anywhere.
>> I agree.
>>>  It was for this, if for nothing else, that I wanted us to have a 
>>> model theory.
>>>  Please, please, lets try to stick with the concepts we have a formal
>>>  mathematical definition for in the model theory.  We have nodes and 
>>> arcs and
>>>  labels.
>> OK, but a slight quibble at this point:  I want the model theory to help
>> define and clarify the concepts we need to be using, but if we find we
>> need other concepts, I want to change the model theory to cover them,
>> not throw out the concepts because they aren't in the model theory.
> I agree, FWIW. However I undertake to try to adapt the MT to suit 
> whatever we decide.

Yes, you do.  Thanks!

>> Now to your point:  I think the model theory has the concepts we need
>> (possibly not using the same terms though).  In the model theory, we
>> also have "asserted triples".  Also, in Section 2.1, there is also the
>> statement: "An arc labeled with p from a node n1 to a node n2 maps [in
>> logic] to an atomic assertion that the relation p holds true between the
>> expressions s and o gotten by translating n1 and n2 respectively [to the
>> appropriate logical constants] (written as (p s o) in KIF syntax)..."  I
>> would say that the thing that is an "assertion" in logic is a
>> "statement" in RDF [assuming we're dealing with only "asserted triples"
>> at the moment.  What is that (p s o) thing in KIF syntax called?]  This
>> was (as I understood it) the basis of all our discussions about the
>> equivalence of RDF to a simple form of EC logic (using only binary
>> properties.  (In fact, if I remember correctly, at one time those things
>> we now call "statements" used to be called "assertions" in RDF).  The
>> point is, we need more than nodes, arcs, and labels, we need things
>> whose denotations are true or false.  The model theory says those things
>> are asserted triples s p o (which I interpret as being the RDF syntax
>> for a statement, like "Ora Lassila created <foo>").  Is the problem
>> whether we're talking about the syntax (the RDF side) versus the
>> interpretation?
> I think that the mapping into logic doesn't help. This type/token 
> distinction runs through all languages. 

I didn't mean to suggest that the mapping to logic helped with the 
type/token business.  I meant to suggest that the mapping to logic 
illustrates that something is needed beyond nodes, arcs, and labels. 
However, it occurs to me that this may not be right, depending on how an 
arc in the graph is understood, i.e., whether the arc includes the two 
nodes at its ends or not.  What occured to me was that I'd been 
interpreting "arc" as simply the connecting line, in which case you need 
another concept for "arc and its beginning and ending nodes" (a triple, 
in other words).  So where the model theory says "An arc labeled with p 
from a node n1 to a node n2 maps to an atomic assertion..." I was 
interpreting that as saying that the thing corresponding to an atomic 
assertion was a group of things, an arc, and two nodes (a triple), not 
just the arc.  And the model theory defines triple too.  Back to 
elementary graph theory.


Frank Manola                   The MITRE Corporation
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mailto:fmanola@mitre.org       voice: 781-271-8147   FAX: 781-271-875
Received on Thursday, 25 October 2001 11:24:38 UTC

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