- From: Graham Klyne <GK@dial.pipex.com>
- Date: Mon, 08 May 2000 10:54:42 +0100
- To: Dan Brickley <danbri@w3.org>
- Cc: www-rdf-interest@w3.org
At 04:16 PM 5/4/00 -0400, Dan Brickley wrote: > > (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...) Dan, It turns out I didn't think hard enough before posting that... I had thought one could express the idea: [A] --PID--> [P] AND [PID] is sub-property of [PID1] IMPLIES [A] --PID1--> [P] using subclassing of property types. But on closer examination it seems that this can't be done. (So thanks for making me think harder ;-) #g -- >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 ------------ Graham Klyne (GK@ACM.ORG)
Received on Monday, 8 May 2000 08:50:55 UTC