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Re: owl:Thing (was Re: Managing Co-reference)

From: Bijan Parsia <bparsia@cs.man.ac.uk>
Date: Thu, 22 May 2008 00:19:26 +0100
Message-Id: <05AAC179-7FEC-48BB-8EE0-1CEBDC1DA957@cs.man.ac.uk>
Cc: "Semantic Web" <semantic-web@w3.org>
To: "Peter Ansell" <ansell.peter@gmail.com>

On May 22, 2008, at 12:04 AM, Peter Ansell wrote:
> I have a feeling I am mixed up with the idea of classes and instances
> and their logic representations. Some of what you say doesn't make
> sense to me, but you are very sure about it so I probably should do
> some more reading. I get hung up on the idea that you even need to
> define a special class for something which can never have any
> instances.

I can give you a reason why you want to have a special name for it:  
It's very handy for indicating unsatisfiable classes ina  UI.

> Am I wrong in saying that you start off with nothing, and them
> immediately use that to define everything, and then have subsets of
> everything, except for in a case where the subset would be nothing and
> it would then be sectioned off into its own world?

I would say that you are wrong. That's certainly not how logics are  

Typically you start off with a definition of the logical connectives  
(e.g., negation, the quantifiers, etc.).

> It just doesn't
> seem meaningful, even though it may be proved consistent once I
> understand classes and individuals and instances etc.

I hope so.

I think you need to let go of this line. Try starting with a text on  
propositional logic. The key bits to look at are tautologies (i.e.,  
theorems) and contradictions.

Received on Wednesday, 21 May 2008 23:20:10 UTC

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