# Re: I have a trouble with The RDF Model

From: pat hayes <phayes@ai.uwf.edu>
Date: Wed, 29 Nov 2000 16:40:00 -0600
Message-Id: <v0421010fb64b3292b01d@[205.160.76.86]>
To: Graham Klyne <gk-lists@dial.pipex.com>
Cc: <www-rdf-logic@w3.org>
```>At 09:44 AM 11/27/00 -0600, pat hayes wrote:
>>The domain of a model theory, more or less by definition of the
>>term "model theory", is the expressions of the language (or perhaps
>>more exactly, the parsings of those expressions according to the
>>syntactic rules of the language.)
>
>I'm not sure I'd know a model theory if it leapt up and bit me, but
>that's a useful start for me.  What would you say is the "range" of
>a model theory?

I'm glad you asked. The range is the interpretations. Thats what a
model theory does: it defines (a mathematical model of) what counts
as an interpretation of the language, and gives rules for how to
interpret the expressions of the language in such an interpretation.
(Other names for interpretations are 'possible world', 'set of
circumstances' 'state of affairs' and 'model of the world'.) Exactly
what counts as an interpretation, speaking now mathematically,
depends on the language; more intricate langauges require more
complicated notions of 'interpretation'. Propositional logic requires
simply an assignment of truth-values to the basic proposition
letters. First-order relational logic requires a set over which the
quantifiers range, and denotations defined over this set for all the
names and relation names in the language. Programming languages have
traditionally required functional domains obeying certain fixpoint
properties. Modal logics require more complicated interpretations
with multiple domains linked by accessibility relations, and so on.
'Ontology' lanugages like DAML, which essentially describe a
heirarchy but don't say anything much about it, seem to require only
some sets with some relations between them as an interpretation, as
in Peter Patel-Schneider's OIL semantics. Right now Im not yet sure
what RDF really needs, but Im working on it.

>>So I repeat: are you saying that the 'at' assertions are part of RDF, or not?
>
>I'd say not, but that it is possible to _model_ the 'at' assertions in RDF.

The trouble with that answer is, I really do not know what it means.
What sense of 'model' are you using? Do you mean it is possible to
*describe* them in RDF? Or that it is possible to *simulate* them in
RDF? Or that they are some kind of assertional *extension* to RDF? Or
*axioms written in RDF syntax*? Any help would be appreciated.

Pat Hayes

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Received on Wednesday, 29 November 2000 17:38:42 UTC

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