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RE: rdfs:class and rdfs:resource

From: Jon Hanna <jon@spin.ie>
Date: Wed, 7 May 2003 19:07:28 +0100
To: "Www-Rdf-Interest" <www-rdf-interest@w3.org>

> Jon
> 1. You say
>     <rdfs:Class> <rdf:type> <rdfs:Class> .
> which is true.  But it also implies that
>     <rdfs:Class> <owl:sameAs> <rdfs:Class> .
> which is really more important.  In other words
>     "every Class is identical to itself"
> is more important and relevant than
>     "every Class is a subClass of itself".

I didn't say that every class is a subclass of class, but that rdfs:Class is
of type rdfs:Class.

> 2. You did not consider whether
>     <#jonsCar> <rdf:type> <rdfs:Class> .
> Of course, it is not, because <#jonsCar> is not a Class.
> That is what makes rdfs:Class different from all other classes.

Yes. I considered this, but what I intended to be a brief mail was getting
long-winded as it is, and left me with a choice of either re-writing as
something more closely approaching an essay, or to excise a few bits.

> There are two ways to resolve this "paradox".
> (I agree with Francesco that it is a "paradox").

I don't. It's a language problem (I'll see Francesco's Russell and raise you
a Wittgenstein :) Luckily this language problem is of a simple type, in that
the problem is in how we describe this to developers, rather than any
inherent problem with language.
If it were truly paradoxical we would have problems explaining it to
machines, and then we would be truly stuck.

Another way to think about this is with comparison to natural language:

"thing" is a word. All words are things, including the word "word" and the
word "thing". If we can categorise something as being a "word" then we can
also categorise it as being a "thing". Hence "word" is a subclass of
"thing". Further, all words are subclasses of "thing".

"thing" is analogous to <rdfs:Resource> and "word" to <rdfs:Class>.
Received on Wednesday, 7 May 2003 14:01:42 UTC

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