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Re: What do the ontologists want?

From: pat hayes <phayes@ai.uwf.edu>
Date: Tue, 15 May 2001 17:52:17 -0500
Message-Id: <v04210114b7275f200991@[]>
To: "Seth Russell" <seth@robustai.net>
Cc: www-rdf-logic@w3.org, ora.lassila@research.nokia.com, swick@w3.org
>From: "pat hayes" <phayes@ai.uwf.edu>
> > First, note that quoting provides a character string, and reification
> > in general provides at most a description of syntactic form, so such
> > 'attribution' examples need to be taken with a pinch of salt. There
> > is a world of difference between "X says 'statement Y'" and "X says
> > that Y". Notice in the second case that the Y is NOT quoted; it is
> > being used (to refer to its content), not mentioned. Reification does
> > not provide access to content, only form.
>Apparently you are not using the word 'reification' in the same sense that
>it is applied to the example below in the RDF specification; see [1].
>    Ralph Swick says that Ora Lassila is the creator
>    of the resource http://www.w3.org/Home/Lassila.
>[1] http://www.w3.org/TR/REC-rdf-syntax/#higherorder

No, I believe I am using it in that sense. The reference you cite 
says the following:

For example, let us consider the sentence

        Ora Lassila is the creator of the resource 

RDF would regard this sentence as a fact. If, instead, we write the sentence

        Ralph Swick says that Ora Lassila is the creator of the 
resource http://www.w3.org/Home/Lassila.

we have said nothing about the resource 
http://www.w3.org/Home/Lassila; instead, we have expressed a fact 
about a statement Ralph has made. In order to express this fact to 
RDF, we have to model the
original statement as a resource with four properties. This process 
is formally called reification in the Knowledge Representation 
community. A model of a statement is called a reified statement.

Notice that this says that reification is used in the sense it is 
used in KRep, that a reified statement is a "model of" a statement, 
which I take it means that it refers to that other statement; and 
that the second fact is "about" the original statement. All of this 
is exactly what I mean by reification also.

However, I think that the authors have used a slightly misleading 
example. Notice that if the second sentence is taken literally, what 
they say about it is not quite true. If understood in the most direct 
way, it *does* say something about the resource 
http://www.w3.org/Home/Lassila; it says, in fact, that Ralph Swick 
says that Ora Lassila is the creator of it. The fact that the authors 
claim that it says *nothing* about the resource suggests that they 
are understanding this sentence to mean something like a direct 
quotation, ie to mean something like: Ralph Swick uttered these 
words: "Ora Lassila is.....". Then, indeed, everything they say about 
the second sentence would be correct: it would say nothing about the 
resource, and it would be correctly modelled by reification. So, I am 
inclined to be charitable and assume that that this what they meant, 
even though it is not what they said. They were not writing a 
philosophical tract, after all.

Pat Hayes

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Received on Tuesday, 15 May 2001 18:52:19 UTC

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