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

From: Brian McBride <bwm@hplb.hpl.hp.com>
Date: 15 Jul 2003 17:45:03 +0100
To: Dan Brickley <danbri@w3.org>
Cc: rdf core <w3c-rdfcore-wg@w3.org>
Message-Id: <1058287502.3413.78.camel@dhcp-91-136.hpl.hp.com>

Hi Dan,

I have reviewed this and it looks good.

Two nits - neither critical.

1) in [[The rdfs:subClassOf property may be used to state that one class
is a subclass of another.]] the rdfs:subClassOf could be linked to the
property definition.

2) A similar sentence for subPropertyOf could be included in the
description of subproperty.

Brian

On Fri, 2003-07-11 at 14:53, 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.
> 
Received on Tuesday, 15 July 2003 12:55:40 EDT

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