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Re: Assessment of RDF Scheme edits needed re rdfs:subClassOf iff -> if

From: Graham Klyne <gk@ninebynine.org>
Date: Fri, 11 Jul 2003 22:14:43 +0100
Message-Id: <5.1.0.14.2.20030711221326.03167668@127.0.0.1>
To: Dan Brickley <danbri@w3.org>, w3c-rdfcore-wg@w3.org

On a cursory read, this looks to me as if it reflects the intended 
intensional semantics, though I can't tell if these are *all* the edits needed.

#g
--

At 09:53 11/07/03 -0400, Dan Brickley wrote:


>I'm working through the edits required on RDF Schema following this
>decision (which I wasn't party to, but support).
>
>In section "2. Classes" of RDFS, we say:
>
>[[
>RDF distinguishes between a class and the set of its instances.
>Associated with each class is a set, called the class extension of the
>class, which is the set of the instances of the class. Two classes may
>have the same set of instances but be different classes. For example,
>the tax office may define the class of people living at the same address
>as the editor of this document. The Post Office may define the class of
>people whose address has the same zip code as the address of the author.
>It is possible for these classes to have exactly the same instances, yet
>to have different properties. Only one of the classes has the property
>that it was defined by the tax office, and only the other has the
>property that it was defined by the Post Office.
>
>A class may be a member of its own class extension and thus may be an
>instance of itself.
>]]
>
>I propose to leave this intact except for striking 'thus' from the
>second sentence.
>
>We go on to say:
>[[
>A class C is a subclass of a class C' if and only if all the instances
>of C are also instances of C'. All classes are subclasses of themselves.
>The rdfs:subClassOf property may be used to state that one class is a
>subclass of another. The term super-class is used as the inverse of
>subclass. A class C' is a super-class of a class C if and only if C is a
>subclass of C'.
>]]
>
>This is the crux of it. As a replacement, I propose:
>[[
>If a class C is a subclass of a class C', then all instances of C will
>also be instances of C'. The rdfs:subClassOf property may be used to
>state that one class is a subclass of another. The term super-class is
>used as the inverse of subclass. If a class C' is a super-class of a
>class C, then all instances of C are also instances of C'.
>]]
>
>Given the new semantics, this as close to a definition as we can easily
>get. We tell the world the consequences of an rdfs:subClassOf relation,
>but we don't have an 'iff' definition anymore, which is necessarily
>going to be a crisper read.
>
>Section "3. Properties",
>[[
>This specification defines the concept of subproperty. A property P is a
>subproperty of property P' if and only if all subjects and objects
>related by P are also related by P'. All properties are subproperties of
>themselves. The term super-property is often used as the inverse of
>subproperty, i.e. P is a super-property of P' if and only if P' is a
>subproperty of P. This specification does not define a top property that
>is the super-property of all properties.
>]]
>needs to become:
>[[
>This specification defines the concept of subproperty. If a property P
>is a subproperty of property P', then all pairs of resources which are
>related by P are also related by P'. The term super-property is often
>used as the inverse of subproperty. If a property P' is a super-property
>of a property P, then all pairs of resources which are related by P
>are also related by P'. This specification does not define a top
>property that is the super-property of all properties.
>]]
>
>Sections "3.4 rdfs:subClassOf" and "3.5 rdfs:subPropertyOf" - no change
>needed.
>
>I believe this is all the edit needed to bring things back into line
>with the semantics. Someone else's attention on this would be much
>appreciated, though I'll commit an updated doc with these changes for
>review.
>
>Thanks,
>
>Dan
>
>
>----- Forwarded message from Dan Connolly <connolly@w3.org> -----
>
>From: Dan Connolly <connolly@w3.org>
>Date: 10 Jul 2003 11:00:19 -0500
>To: www-webont-wg@w3.org
>Cc: Brian McBride <bwm@hplb.hpl.hp.com>
>Subject: RDFCore changed rdfs:subClassOf from iff to if
>Message-Id: <1057852819.16090.432.camel@dirk.dm93.org>
>Resent-From: www-webont-wg@w3.org
>Resent-Date: Thu, 10 Jul 2003 12:36:27 -0400 (EDT)
>Organization: World Wide Web Consortium (http://www.w3.org/)
>
>
>As I mentioned briefly last week...
>http://www.w3.org/2003/07/03-webont-irc#T17-26-38
>
>RDF Core has decided to change the semantics of rdfs:subClassOf
>and subPropertyOf...
>
>[[
>10: Issue horst-01
>
>DECISION: to close horst-01 by moving to intensional semantics for
>subClassOf ('if' rather than 'if and only if'), and by including new
>rules rdfs12a and rdfs12b in additional part of rules section.
>[...]
>
>ACTION: DanC to inform WebOnt. context,
>http://www.w3.org/2003/06/27-rdfcore-irc#T15-21-11
>
>ACTION: PatH to respond to the commentor (ter horst). context,
>http://www.w3.org/2003/06/27-rdfcore-irc#T15-21-48
>]]
>
>I think the only impact is on S&AS, and Peter said
>he was well prepared for it; he'd only have to
>un-comment some stuff from his source.
>
>
>--
>Dan Connolly, W3C http://www.w3.org/People/Connolly/
>
>
>----- End forwarded message -----

-------------------
Graham Klyne
<GK@NineByNine.org>
PGP: 0FAA 69FF C083 000B A2E9  A131 01B9 1C7A DBCA CB5E
Received on Friday, 11 July 2003 17:40:37 EDT

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