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Re: Ill-typed vs. inconsistent?

From: Antoine Zimmermann <antoine.zimmermann@emse.fr>
Date: Fri, 16 Nov 2012 12:27:55 +0100
Message-ID: <50A6233B.6020903@emse.fr>
To: Pierre-Antoine Champin <pierre-antoine.champin@liris.cnrs.fr>
CC: "public-rdf-wg@w3.org" <public-rdf-wg@w3.org>

Le 14/11/2012 21:41, Pierre-Antoine Champin a écrit :
<skip>

>>>
>>> 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.
>>
>
> I don't see how my proposal above makes the notion of type more present
> than it was before:
> * typed literals are a subset of V, they were already there
> * LV is a distinguished subset of IR in *all* interpretation, it was
> already there.

Ok, point taken.

>
> I don't believe (nor intend) that the proposal above changes the result of
> simple entailment.

True.

> The only change is that, in order to satisfy the following graph:
>
>    :a :b "foo"^^xsd:integer .
>
> an interpretation will have to verify
>
>    IL("foo"^^xsd:integer) is in LV
>
> As nothing, in simple entailment, can constrain LV in any way,
> nothing prevents a graph consistent with the current condition to have a
> satisfying interpretation that meets the condition I propose.
>
> On the other hand, under XSD-entailment, as "foo" is not a valid lexical
> form for xsd:integer,
> the semantic conditions for datatypes impose to every interpretation that
>
>    IL("foo"^^xsd:integer) is not in LV
>
> so no XSD-interpretation can satisfy the graph above under the condition I
> propose.
>
>
> Again, what I'm trying to model is the intuition that any typed literal is
> claiming that its lexical form is indeed a lexical value of its datatype
> (in rdf-mt parlance: they denote something in LV). This claim is neutral in
> simple-entailment, where datatypes have no special meaning (LV is not
> constrained). It has some impact in D-entailment (reflected in rdf-mt by
> the semantic conditions for datatypes that constraing what can and cannot
> be in LV).
>
> Or do you object to this intuition? I had the impression that your proposal
> was going that way too...
>
> 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.
>>
>
> That can work of course.
> But that makes RDF+XSD a sublanguage of RDF, just like OWL-DL is.
> Worse, that makes RDF+D (with D any set of datatypes) a different
> sublanguage.

Yes.

> Makes me feel uneasy.

Not me. I like it in fact, and it does not prevent applications that 
support a datatype to actually handle ill-typed literals and so, 
effectively work on full RDF. The syntactic restrictions of OWL DL do 
not prevent DL tools from supporting most RDF graphs (e.g., Protégé 4, 
and OWL 2 *DL* editor, can load any RDF files; Pellet, HermiT, FacT++, 
etc can reason on a significant set of non-OWL-DL ontologies).
I also suspect that there are Turtle parsers that can parse certain 
syntax errors (e.g., interpreting rdf:type correctly when the prefix 
rdf: is not defined).



AZ

>
>    pa
>
>
>
>> 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.
>>
>>
>>
>> AZ
>>
>>
>>> 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
>> France
>> Tél:+33(0)4 77 42 66 03
>> Fax:+33(0)4 77 42 66 66
>> http://zimmer.aprilfoolsreview.com/
>>
>>
>

-- 
Antoine Zimmermann
ISCOD / LSTI - Institut Henri Fayol
École Nationale Supérieure des Mines de Saint-Étienne
158 cours Fauriel
42023 Saint-Étienne Cedex 2
France
Tél:+33(0)4 77 42 66 03
Fax:+33(0)4 77 42 66 66
http://zimmer.aprilfoolsreview.com/
Received on Friday, 16 November 2012 11:28:23 GMT

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