Fwd: rdfs:Class vs owl:Class

Forwarded with Hans' permission:  As I mentioned to this WG, this  
sort of question arises a lot - and not from people with no  
background - this is a good example of why, given we seem unable to  
fix the problem (I'd hoped punning might), that we should at least  
document the discussion more carefully
  -JH


Begin forwarded message:

> From: "Hans Teijgeler" <hans.teijgeler@quicknet.nl>
> Date: December 6, 2007 1:42:54 AM EST
> To: "Hendler, Jim" <hendler@cs.rpi.edu>
> Subject: rdfs:Class vs owl:Class
>
> Hi Jim,
>
> I'm involved in OWL for some years now, and I am still in the dark  
> when to use rdfs:Class and when owl:Class (or whether to use  
> rdfs:Class at all).
>
> In the W3C Recommendation "OWL Web Ontology Language Reference",  
> par. 3.1 I read: "NOTE: owl:Class is defined as a subclass of  
> rdfs:Class. The rationale for having a separate OWL class construct  
> lies in the restrictions on OWL DL (and thus also on OWL Lite),  
> which imply that not all RDFS classes are legal OWL DL classes. In  
> OWL Full these restrictions do not exist and therefore owl:Class  
> and rdfs:Class are equivalent in OWL Full.".
>
> But nowhere can I find which RDFS classes are illegal OWL DL  
> classes. Do you know where to find that? What do they (you  
> included) mean with 'RDFS classes' in this sentence?
>
> I am also in the dark why I can have <rdfs:Class rdf:ID="Opera"/>  
> as well as <owl:Class rdf:ID="Opera">. What is the essential  
> difference?
>
> In the OWL documents the user plays an important role, whereas in  
> the RDF Schema document the word 'user' does not occur at all.  
> Isn't <rdfs:Class rdf:ID="Opera"/> a user-defined RDFS class?
>
> Is there anything I can do with rdfs:Class that I cannot do with  
> owl:Class? And the reverse?
>
> Can I have an owl:Restriction for an rdfs:Class?
>
> Do you see any flaws in attached graph?
>
> I hope you can help me with some simple answers.
>
> Regards,
> Hans
>
> ____________________
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> Hans Teijgeler
> Laanweg 28
> 1871 BJ Schoorl
> The Netherlands
> +31-72-509 2005
> hans.teijgeler@quicknet.nl
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>
>
>
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"If we knew what we were doing, it wouldn't be called research, would  
it?." - Albert Einstein

Prof James Hendler    http://www.cs.rpi.edu/~hendler
Tetherless World Constellation Chair
Computer Science Dept
Rensselaer Polytechnic Institute, Troy NY 12180