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Re: Show me the money - (was Subjects as Literals)

From: Antoine Zimmermann <antoine.zimmermann@deri.org>
Date: Thu, 01 Jul 2010 20:56:41 +0100
Message-ID: <4C2CF2F9.7030606@deri.org>
To: Tim Finin <finin@cs.umbc.edu>
CC: Linked Data community <public-lod@w3.org>, Semantic Web <semantic-web@w3.org>
Dear Tim,

Le 01/07/2010 20:03, Tim Finin a écrit :
> On 7/1/10 2:51 PM, Henry Story wrote:
>  > ...
>> So just as a matter of interest, imagine a new syntax came along that
>> allowed literals in
>> subject position, could you not write a serialiser for it that turned
>> "123" length 3 .
>> Into
>> _:b owl:sameAs "123";
>> length 3.
>> ?
>> So that really you'd have to do no work at all?
>> Just wondering....
> Isn't owl:sameAs defined to be a relation between two
> URI references?

Not exactly. OWL DL defines this restriction on owl:sameAs, but 
owl:sameAs is not itself defined like this. Plus, OWL DL is 
syntactically a restriction of OWL (Full) (that is, a syntactic 
restriction of RDF). The current discussion is about RDF, so I don't see 
any reason to mention the specificities of OWL DL here. OWL DL, in any 
case, would forbid literals in subject position.

  Even if not, it is symmetric and
> would have the above imply {"123" owl:sameAs _:b .}

No it does not imply this because "this" is not in the language. The 
language RDF tells you that triples (the formulas in that language) have 
no literals as subjects. In any logical formalism, you cannot infer 
things that are not in the language.

This is actually what is strange about not allowing literals in the 
subject position: you cannot say things like:

"123" owl:sameAs "123"

and therefore, you cannot infer it. If, for any reason, you want to 
infer this, it means that you are in need of a modification of the RDF 
language which allows literal in the subject position.

Yet, to make things more confusing, the interpretation of the predicate 
owl:sameAs, under the OWL semantics, is reflexive and symmetric.

I am preparing an email about the weird consequences of excluding 
literals in subject position.

Antoine Zimmermann
Post-doctoral researcher at:
Digital Enterprise Research Institute
National University of Ireland, Galway
IDA Business Park
Lower Dangan
Galway, Ireland
Received on Thursday, 1 July 2010 19:57:19 UTC

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