- From: Dan Brickley <danbri@w3.org>
- Date: Thu, 4 May 2000 16:16:33 -0400 (EDT)
- To: www-rdf-interest@w3.org
On Thu, 4 May 2000, Graham Klyne wrote: > Another approach, I understand, is to define a new class with multiple > rdfs:subClassOf properties, and use that for the domain and/or range of a > property. Yep, that'd be another modeling style that might appeal in some cases. > (But I'm still not entirely clear when to use rdfs:subPropertyOf vs > rdfs:subClassOf.) Does this attempt help?: (some of this can sound a bit zen, "rdfs:class is an rdfs:class" etc...) If you have a vocabulary resource such as dc:title that is a property, ie. a member of the rdfs:Class rdf:Property, it is the sort of thing that can used as a label on an arc (in the graph representation of RDF). It is a particular type of binary relationship that can hold between resources. If you have a resource such as wordnet:Person that is a class, ie. a member of the rdfs:Class we call rdfs:Class, it is the sort of thing that will itself have members or instances, eg. person-3343, employee-234234 might be considered instances of that class. Sometimes a modeler will decide to represent something as a relationship type (eg. 'title','creator') and sometimes as a class of things (eg. 'Person', 'Mammal'). This is similar to the "do I use elements or attributes" question familiar from XML/SGML, except the mismatch between the technology decisions and modeling style is somewhat gentler. There decision here affects whether they express "specialisation/generalisation" relationships using sub-class or sub-property mechanisms. When you want to express property specialisation relationships (eg. that dc:creator is more specific than, but implies, the dc:contributor relation), you're expressing a sub-property relationship between properties. When you want to express class specialisation relationships (eg. that all resources that are of rdf:type wordnet:Person are also of rdf:type wordnet:Mammal), you use sub-class. The difference is that there's no notion of an instance of the property dc:contributor (exept perhaps its occurence in an RDF statement) but there is a notion of an instance of the class wordnet:Person. So we have different relationships that do similar, but distinct, work. Dan -- mailto:danbri@w3.org
Received on Thursday, 4 May 2000 16:16:35 UTC