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Re: RDF Recommendation Set comments (re agenda for 6th April)

From: Antoine Zimmermann <antoine.zimmermann@insa-lyon.fr>
Date: Wed, 06 Apr 2011 19:34:47 +0200
Message-ID: <4D9CA437.4040605@insa-lyon.fr>
CC: RDF WG <public-rdf-wg@w3.org>
Le 06/04/2011 18:22, Pat Hayes a écrit :
> On Apr 6, 2011, at 10:19 AM, fensel wrote:
>> At 13:39 06.04.2011, Pierre-Antoine Champin wrote:
>>> On 04/06/2011 05:14 AM, Pat Hayes wrote:
>>>> We might want to think about incorporating some version of sameAs
>>>> into RDFS, as this seems to be fundamental to linked data and also
>>>> widely misused. Having the real meaning of equality exposed in the
>>>> RDF standard itself might be doing the world a favor. (?)
>>> +1e99
>> I think this may be a very bad idea. You would force all languages
>> layering on top of RDF to include equality.
> It depends what you mean by 'include'. A language based on RDF can always declare that it will use some other term and refuse to accept the RDF one, just as OWL uses owl:Thing rather than rdf:Resource.  BUt it would be more useful and more in the spirit of interoperability to use the same term and just acknowledge that it is not using all the intended meaning of that term.

I'd say that the comparison with OWL is not particularly appropriate. 
OWL Full is an extension of RDFS and as such, preserves the meaning of 
all the RDF/RDFS vocabularies. rdfs:Resource means the same in OWL Full. 
owl:Thing does not replace it.

OWL DL is not an extension of RDFS and it does not try to replace 
rdfs:Resource by owl:Thing. rdfs:Resource simply has no meaning in OWL 
DL while owl:Thing has a much more specific meaning than "the class of 
all resources". OWL DL is very different thing from RDF which just 
happens to be serialisable in RDF.

>> There are reasons
>> to prevent equality because it turns unification from a syntactical
>> operation into reasoning.
> Only if you claim to be logically complete. A reasoner can always just ignore the equalities, or use them in a limited but useful way. Reasoners are not *obliged* to squeeze every last drop of meaning from all the RDF they encounter. Still, the RDF means what it means :-)

I don't think this is a good way of doing things in a standardisation 
working group. People can always disregard standards or parts of it, of 
course. But going further in this direction, why not adding the whole 
OWL 2 vocabulary to RDF since reasoners are not obliged to implement it?
The WG should not define things that have a risk of being disregarded by 

If one implements a system that deals with RDF, it's ok if it includes 
bits from RDFS but not all. Similarly, if an implementation is doing 
RDFS reasoning, it's ok if it include bits of OWL reasoning. But if one 
wants to define an extension of RDFS, it's not ok that a portion of it 
is disregarded. So, I'd say that adding owl:sameAs to RDFS is a pretty 
strong extension that needs to be pondered carefully and I find Dieter's 
concern quite reasonable.

> Pat
>> Dieter
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Antoine Zimmermann
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Database Group
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Received on Wednesday, 6 April 2011 17:35:30 UTC

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