On Jul 6, 2012, at 5:42 PM, Michael Brunnbauer wrote: (01)
>
> Hello Chris,
>
> Forget it, my remark was nonsense. If I write x rdf:type y or
> y rdf:type rdfs:Class then y is a first class entity. (02)
In RDF, yes, exactly. But the OWL-DL is really a classical description logic
"grafted" onto RDF syntax, and the grafting process has left some ugly scars.
The official normative syntax and semantics for OWL-DL is defined
independently of RDF, and has its own notions of first-class-ness based on a
strict individual/class/property segregation. (03)
>
> But I don't think any RDF/RDFS/OWL semantics sees classes as sets. The RDFS
> semantics entails rdfs:Class rdf:type rdfs:Class. (04)
RDF/RDFS/OWL-Full don't see classes as sets. OWL-DL does. (05)
Pat (06)
>
> Regards,
>
> Michael Brunnbauer
>
> On Fri, Jul 06, 2012 at 04:25:13PM -0500, Chris Menzel wrote:
>> On Fri, Jul 6, 2012 at 4:05 PM, Michael Brunnbauer
><brunni@xxxxxxxxxxxx>wrote:
>>
>>>
>>> Hello Matthew,
>>>
>>> On Fri, Jul 06, 2012 at 09:35:02PM +0100, Matthew West wrote:
>>>> CM> ... classes are extensional in OWL.
>>>> Is that extensional in that the extension is the members declared in the
>>> OWL ontology, or is that extensional in the sense that the members define
>>> the class, but I might not know about all of them?
>>>
>>> I think it's extensional in the sense that classes are not first class
>>> entities
>>> but defined via the extension of the rdf:type property.
>>>
>>> http://www.w3.org/TR/rdf-mt/#sinterp
>>>
>>
>> Actually, yes, there is an RDF-compatible semantics for OWL I'd forgotten
>> about where OWL classes are simply entities that are assigned sets of
>> individuals as their extensions. In this semantics, distinct classes can
>> have the same "members". But IIRC in both the W3C "direct" semantics for
>> OWL and the "model theoretic" semantics, OWL classes are simply sets of
>> individuals.
>>
>> Pat will probably jump in here and straighten me out...
>>
>> -chris
>
>>
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