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Re: Ill-typed vs. inconsistent?

From: Antoine Zimmermann <antoine.zimmermann@emse.fr>
Date: Wed, 14 Nov 2012 15:48:27 +0100
Message-ID: <50A3AF3B.80800@emse.fr>
To: public-rdf-wg@w3.org
Le 14/11/2012 11:19, Pierre-Antoine Champin a écrit :
> Pat,
> On Wed, Nov 14, 2012 at 8:16 AM, Pat Hayes<phayes@ihmc.us>  wrote:
>> What I still don't follow is, why anyone who understands what an
>> inconsistency is, would even form the idea that an ill-typed literal would
>> be an inconsistency. It's not the distinction that needs explaining, it's
>> why anyone would treat them as similar in the first place.  Illformedness
>> is not even in the same category as an inconsistency. Literals aren't true
>> or false by themselves.
> I think the divergence of opinion comes from the fact that
> * you see typed literals merely as terms (which, strictly speaking, they
> are), and a term can not be False; it just denotes something ;
> * others (at least myself!) see a little more in them, namely: an implicit
> assertion that the denoted thing is indeed in the value space of the
> datatype.
> If we decide to bite that bullet, then this could be endorsed in the
> semantic condition for a *graph*:
>    if E is a ground RDF graph then I(E) = false if I(E') = false for some
> triple E' in E,
>    or if I(E') is not in LV for some typed literal E' in V,
>    otherwise I(E) =true.

Ouch. I don't like the fact that the notion of type comes in at the 
level of ground-graph simple entailment.

The more I think of this issue, the more I believe that ill-typed 
literals should be a syntax error. An application that supports a 
datatype should reject RDF graphs that do not write literals of that 
type properly.

Note that in OWL 2 Structural Specification and Functional Style Syntax, 
it is required that:

"The lexical form of each literal occurring in an OWL 2 DL ontology MUST 
belong to the lexical space of the literal's datatype."

cf. Section 5.7 http://www.w3.org/TR/owl2-syntax/#Literals.


> The first line (from the original definition) accounts for everything
> asserted explicitly in a triple,
> while the second line (which I added) accounts for those "implicit"
> assertions carried by typed literals.
> Do you think it's a clean way to do it? Or do you consider it as just
> another "trick" ? :-)
>    pa

Antoine Zimmermann
ISCOD / LSTI - Institut Henri Fayol
École Nationale Supérieure des Mines de Saint-Étienne
158 cours Fauriel
42023 Saint-Étienne Cedex 2
Tél:+33(0)4 77 42 66 03
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Received on Wednesday, 14 November 2012 14:48:51 UTC

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