W3C home > Mailing lists > Public > www-rdf-logic@w3.org > May 2001

Re: What do the ontologists want?

From: pat hayes <phayes@ai.uwf.edu>
Date: Tue, 15 May 2001 14:32:40 -0500
Message-Id: <v0421010ab72732447f4e@[205.160.76.173]>
To: Uche Ogbuji <uche.ogbuji@fourthought.com>
Cc: www-rdf-logic@w3.org
> > > From: pat hayes [mailto:phayes@ai.uwf.edu]
> > > [Jonathan Borden wrote:]
> > > > Certainly being able to quote statements/triples is useful
> > > > ... indeed a practical requirement.
> > >
> > > Can you (or anyone) say why the ability to quote is considered a
> > > practical necessity? From where I am standing it seems an arcane and
> > > exotic ability, not one that is of central practical importance. What
> > > is the practical utility of being able to refer to a predicate,
> > > rather than use it?
> >
> > I've got sympathies on both sides of this, based on past and 
>present systems
> > I've used; summarised below.  I'm also pretty hard-nosed about 
>why I'm doing
> > this; summarised in the last paragraph.
> >
> > Some systems are more obvious to design if there is a facility to make a
> > statement about a statement.  Almost always, these are attributions: the
> > typical example seen on this list, and the examples we used in SMK, are of
> > the form "X says 'statement Y'".  (Question: Can anyone come up with a
> > different use for reification?  If this is the only special-case, should
> > there be a different mechanism for attribution?)

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.

>?  The RDF spec itself has a different use case.  Furthermore, all the uses
>are pretty old hat (at least on www-rdf-interest).  I'm sure I'm mising
>something, but just in case, general categories include
>
>Attribution: your "Midwinter Spring is its own season", says Eliot

See above.

>Quantification: Temperatures are in the high 30s (in degrees centigrade)

This is just a mistake. Reification cannot introduce quantifiers into 
a language. At best it can describe the syntax of quantified 
statements (even that requires a more extensive set of 
reification/quoting tools than RDF provides), but it does not - 
indeed, provably cannot - describe the semantics of quantification.

>Qualification: "The check's in the mail", he lied (OK, it's
>attribution+qualification, but I like the example)

This refers to the content of the reified statement, not its form.

>Examples that fall into the above bin include
>
>Temporal placement:  1980: The capital of Nigeria is Lagos; 1990: The capital
>of Nigeria is Abuja

Again, this has nothing to do with reification. It belongs in the 
area of temporal logic.

>Confidence factors: There is a 15% likelihood that Malaria results in death.

Also nothing to do with reification. Notice the use of "that" which 
is a linguistic marker for content rather than form.

All of the above, with the possible exception of the Eliot quotation 
example (which havers between direct and indirect quotation by its 
literary usage of "says"), involve reference not to the form of an 
expression, but to its meaning or content. The way to refer to the 
meaning of an expression is to USE it, not to MENTION it, which is 
what quotation/reification do.

RDF usage of reification is built on a fundamental mistake: the 
confusion between use and mention in linguistic analysis.

Pat Hayes

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Received on Tuesday, 15 May 2001 15:32:43 UTC

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