RE: [OEP] "Classes as values": comments on draft

I wanted to offer some comments on the draft which is at [1].

Dan Brickley, myself and others had an extended discussion this week about
this issue.  I would like to offer the following suggestion as a
recommendation re the use of dc:subject.

I believe the best way to express the fact that a particular image depicts a
thing which is a member of the class of Lions would be to say: 

LionImage
	a	AnimalImage;
	foaf:depicts	[a	Lion].

Lion
	a	owl:Class;
	subClassOf	Mammal;

Mammal	a	owl:Class;
AnimalImage	a	owl:Class;


The alternative way of expressing similar information is to use the
dc:subject property along with the SKOS model [2] for describing concepts
that are intended to act as 'subjects' or 'topics' for information
resources.

LionImage
	a	AnimalImage;
	dc:subject	LionConcept;

LionConcept
	a	skos:Concept;
	skos:prefLabel	'Lions';
	skos:broader	MammalConcept;

MammalConcept
	a	skos:Concept;
	skos:prefLabel	'Mammals';
	skos:narrower	LionConcept;

The SKOS vocab already defines a class 'Concept' and a set of properties for
organising concepts into a hierarchy, without demanding that the hierarchy
implies a subclass relationship.  I refer the WG to the document [2] which
outlines the SKOS-Core schema, although you should currently ignore the
final section on 'using SKOS-Core with DC and FOAF' as this will change
shortly to be in line with the model of usage that I have briefly described
here.

Yours,

Alistair.

[1]
http://lists.w3.org/Archives/Public/www-archive/2004Apr/att-0061/ClassesAsVa
lues.html
[2] http://www.w3.org/2001/sw/Europe/reports/thes/1.0/guide/