RE: RDF Extensibility

Dan Brickley wrote:

>2010/7/6 Jiří Procházka <>:
>> On 07/06/2010 03:35 PM, Toby Inkster wrote:

>>> It would have a meaning. It would just be a false statement. The
>>> same as the following is a false statement:
>>>       foaf:Person a rdf:Property .
>> Why do you think so?
>> I believe it is valid RDF and even valid under RDFS semantic
>> Maybe OWL says something about disjointness of RDF properties and
>> URI can be many things.
>It just so happens as a fact in the world, that the thing called
>foaf:Person isn't a property. It's a class.

The semantics of RDFS allows to use the same name for both a class and a

What you call a "fact in the world" is, from a semantics point of view, just
one particular interpretation that you have in mind. Other interpretations
than yours are possible (I hope :)). And the (model-theoretic) semantics of
RDFS is of a form that a given RDF statement is false, only if /all/
possible interpretations are false. (This is not specific to the RDF
semantics, btw.)

>Some might argue that there are no things that are simultaneously RDF
>classes and properties, but that doesn't matter for the FOAF case. 

Let's not forget that we are here discussing a suggested change of the
syntax and (possibly) semantics of the RDF specification, and the FOAF case
doesn't matter for this, I would say. FOAF refers to RDFS (and OWL), not the
other way round (except, perhaps, as a usecase). Of course, one could define
an extension of the RDFS semantics specifically for FOAF that better
reflects the intended situation (either formally or informally, or
implicitly by a reference implementation of a specific FOAF reasoner). But
that's a different discussion.

>RSS1 vocabulary btw tried to define something that was both,
>rss1:image I think; but this was a backwards-compatibility hack.

You might find more of these "hacks" elsewhere, and more to come in the
future. Interestingly, the idea of using the same name for both a class and
a property is somewhat that has been introduced in OWL DL just in OWL 2, so
it exists in OWL DL for less than a year now (officially). In RDFS and
(therefore) in OWL Full, it has always been allowed, though.



Dipl.-Inform. Michael Schneider
Research Scientist, Information Process Engineering (IPE)
Tel  : +49-721-9654-726
Fax  : +49-721-9654-727
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Received on Tuesday, 6 July 2010 15:55:34 UTC