- From: Ralph R. Swick <swick@w3.org>
- Date: Tue, 21 Sep 1999 13:52:04 -0400
- To: Pierre-Antoine CHAMPIN <champin@cpe.fr>
- Cc: <www-rdf-comments@w3.org>
At 10:15 AM 8/17/99 +0100, Pierre-Antoine CHAMPIN wrote: http://lists.w3.org/Archives/Public/www-rdf-comments/1999JulSep/0024 > <rdf:Property rdf:id="P1"> > <rdfs:range rdf:resource="#C1"/> > </rdf:Property> > > <rdf:Property rdf:id="P2"> > <rdfs:subPropertyOf rdf:resource="#P1"/> > <rdfs:range rdf:resource="#C2"/> > </rdf:Property> > > in this case, it seems logic to me that C2 must be a subclass of C1, > (or at most to be the SAME class, of course). > > Though, this constraint is not explicitely imposed by RDF, or am I wrong ? RDF Schema does not state that you can infer a subclass relationship here; a resource can be an instance of more than one class without there being any subclass relationship between those classes. http://www.w3.org/TR/1999/PR-rdf-schema-19990303 says (Section 2.3.3) "If some property P2 is a subPropertyOf another more general property P1, and if a resource A has a P2 property with a value B, this implies that the resource A also has a P1 property with value B." Therefore B must be a permissible value for -- i.e. in the range of -- both P1 and P2. For a specific value B1 to be a permitted value of P1 it must have type C1 and similarly to be a permitted value of P2 it must have type C2: {rdf:type, B1, #C1} {rdf:type, B1, #C2} Now, B1 can have both types without either C1 or C2 being a subclass of the other. (Section 2.3.1: "A resource may be an instance of more than one class.") It is certainly true (by Section 2.3.2) that if the statement {rdfs:subClassOf, #C2, #C1} does exist in the graph then the statement {rdf:type, B1, #C1} is implicit. But the RDF Schema specification specifically does require that C2 be a subclass of C1. Consider a class WritingInstrument and a class PaintBrush. Obviously a brush used for calligraphy could be an instance of both classes but not all brushes are considered to be writing instruments. -Ralph
Received on Tuesday, 21 September 1999 13:52:43 UTC