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Re: RDF Issue rdfs-clarify-subClass-and-instance

From: Piotr Kaminski <piotr@ideanest.com>
Date: Wed, 21 Aug 2002 14:11:02 -0700
To: graham wideman <graham@wideman-one.com>
Cc: www-rdf-comments@w3.org
Message-id: <02af01c24958$4c7cc430$ada15018@transfinity>

Let me answer Graham's question directly:

> -- What features does a resource have?

None.  Think "Object" in Java, but without any methods.

> -- What features beyond this does a class resource have?

Conceptually, a class has an extension of its instances, which may be empty.
Within the RDF syntax, though, a class has no extra primitive features.

> -- What features beyond this does Class have?

None.  rdfs:Class is just a class, with the usual extension.  Its definition
is that it's the class of classes, i.e. its instances are classes.  It is an
instance of itself.  Think java.lang.Class.

> -- What features does rdf:type transmit from one resource to another?

It makes the object into an instance of rdfs:Class, if it wasn't already.
It makes the subject a member of the extension of the object (the class).
This may carry further consequences for other properties that are defined in
terms of the extension of a class (e.g. rdfs:domain and rdfs:range), but
does not in and of itself change the subject resource.

> And maybe this involves "if the value is Class then rdf:type also
transmits X, Y, Z".

No extra consequences.  If the object is rdfs:Class, then we like to
casually say that the subject "is a class", but this carries no extra
meaning.

> -- What features does subClassOf transmit from one class to another?

If A rdfs:subClassOf B then the extension of A is a subset of the extension
of B.  Also, both A and B are instances of rdfs:Class (either they were
already, or this statement makes them become such).

        -- P.

--
  Piotr Kaminski <piotr@ideanest.com> http://www.ideanest.com
  It's the heart afraid of breaking that never learns to dance
Received on Wednesday, 21 August 2002 17:25:18 GMT

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