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Re: owl:sameAs use/misuse/abuse Re: homonym URIs

From: Jacek Kopecky <jacek.kopecky@deri.org>
Date: Mon, 25 Jun 2007 01:01:10 +0200
To: Richard Cyganiak <richard@cyganiak.de>
Cc: Bernard Vatant <bernard.vatant@mondeca.com>, Tim Berners-Lee <timbl@w3.org>, semantic-web@w3.org
Message-Id: <1182726070.3417.11.camel@localhost>

Wow. It's a nice description of the difference between the symbol and
its referent. But I guess I should be able to state that 

@prefix ex <http://example.org/>
ex:A http:redirects303To <http://example.org/A/doc>
ex:B http:redirects303To <http://example.org/B/doc>
ex:A owl:sameAs ex:B

(which I think was Bernard's point)

Or is it wrong to create http:redirects303To as a statement about the
HTTP resource? If so, why? Or does it perhaps show that while so very
convenient, http: URIs (without fragment ID) already introduce a pun
that makes owl:sameAs too strong?

I've always been uneasy about the 303 approach to having http: URIs
denote non-information resources; I guess I'd be in the 'hash' camp.
Basically, my feeling is that 303 does not fully solve the issue, so it
should be a softer recommendation than a W3C Recommendation MUST. I'm
off-line at the moment though so I can't verify whether the WebArch
document makes a MUST-level statement about information resources and
200 vs. 303 responses.

Having endless fun with the subtleties of SemWeb,
Jacek Kopecky

On Fri, 2007-06-15 at 16:23 +0200, Richard Cyganiak wrote:
> Bernard,
> On 15 Jun 2007, at 10:30, Bernard Vatant wrote:
> > But is not 'A owl:sameAs B' intended to mean, by OWL definition,  
> > that in any context using the semantics of URIs, those semantics  
> > are the same for A and B, so whatever assertion is true of  A is  
> > true of B, so A and B can be used indifferently.
> Huh? No. A and B are *symbols*. They are two different symbols. They  
> cannot be used indifferently.
> The symbols A and B denote two *referents* A' and B' (glossing over  
> the question how exactly they denote those referents). A owl:sameAs B  
> means that anything that is true for A' is true for B' and vice  
> versa. You can use A' and B' indifferently (because they are the  
> same, if you choose to believe the owl:sameAs claim), but not A and B.
> We communicate using symbols. In natural language, in RDF, and in  
> OWL. Changing the symbols changes what is communicated, even if the  
> symbols denote the same thing.
> > But if through http protocol  you retrieve "what the owner of A  
> > declares is true of A" and "what the owner of B declares is true of  
> > B" (read : RDF descriptions of A and B), with no certitude  
> > whatsoever if those descriptions are consistent or not, that means  
> > http protocol is not a context where A and B have the same semantics.
> ´A and B have the same semanticsĦ is a very murky statement best  
> avoided.
> HTTP deals only with symbols (URIs), descriptions of referents (where  
> the referent is a non-information resource), and representations of  
> referents (where the referent is an information resource). It never  
> deals with the referents themselves.
> Two symbols having different descriptions doesn't preclude me from  
> interpreting them as having the same referent. The same-ness of  
> referents never enters the picture at the HTTP level.
> > I can live with that, but it seems at least hard to understand and  
> > harder to explain, if one judge by the everthread about it.
> > OTOH, if one uses owl:sameAs for URIs identifying resources which  
> > are *information resources*, then they should actually redirect to  
> > the same document. Yes?
> That would be a good idea, though technically I don't believe you  
> *have to*.
> Richard
Received on Monday, 25 June 2007 03:55:09 UTC

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