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Re: RDF-ISSUE-109 (ill-typed-so-what): What's the consequence of a literal being ill-typed? [RDF Concepts]

From: Pat Hayes <phayes@ihmc.us>
Date: Tue, 13 Nov 2012 01:50:02 -0800
Cc: Richard Cyganiak <richard@cyganiak.de>, Pierre-Antoine Champin <pierre-antoine.champin@liris.cnrs.fr>, RDF Working Group <public-rdf-wg@w3.org>
Message-Id: <0589EC99-985D-461E-AE05-AB99B38F459C@ihmc.us>
To: Antoine Zimmermann <antoine.zimmermann@emse.fr>

On Nov 13, 2012, at 1:31 AM, Antoine Zimmermann wrote:

> Le 13/11/2012 09:31, Pat Hayes a écrit :
>> 
>> On Nov 12, 2012, at 5:41 AM, Richard Cyganiak wrote:
>> 
>>> ... But that's all besides the point. My question was why the specs
>>> distinguish between the two things in the first place. Even in XSD
>>> entailment, this is consistent:
>>> 
>>> :a :b "xxx"^^xsd:integer.
>>> 
>>> But this is not:
>>> 
>>> :a :b "xxx"^^xsd:integer. :b rdfs:range rdfs:Literal.
>>> 
>>> I don't understand the point of singling out the concept of the
>>> “ill-typed literal”, declaring it to be a “non-syntactic error”,
>>> but not declaring it to be an inconsistency.
>>> 
>> 
>> You completely miss the point. Nothing is being "singled out" in the
>> 2004 design. Inconsistency isn't something you get to "declare", it's
>> a word with a technical meaning. It means, the graph is false in
>> every interpretation. You get to define truth conditions on triples,
>> and then consistency is a product of that.
>> 
>> So, you want
>> 
>>> :a :b "xxx"^^xsd:integer.
>> 
>> to be always false in any XSD-interpretation, no matter what :a and
>> :b are interpreted to mean, right? That is what it means to say that
>> this triple is XSD-inconsistent.
>> 
>> I don't think this is possible without tweaking the basic RDF
>> semantic rules.
>> 
>> Here's the only way I can see of doing it. We require the universe of
>> every interpretation to contain a special semantic value called
>> "error", and we stipulate that no relational extensions ever contain
>> a pair <x, error>, and we also tweak the blank node conditions so
>> that bnodes are never mapped to error. Then we say that any
>> ill-formed literal is required to denote error. This ensures that all
>> triples with an ill-formed literal will be false, so such graphs are
>> always inconsistent. Note, this has to be done in the basic RDF
>> semantics, not just in the XSD semantics, since adding datatypes to
>> literals doesn't change what URIs like :a and :b mean.
> 
> I was thinking of something else:
> 
> if <d> is an IRI in the datatype map, then for any character string aaa in the vocabulary V, < I(aaa^^<d>),I(<d>) > in IEXP(I(rdf:type)).
> 
> For instance, if we have:
> 
> <s> <p> "xyz"^^xsd:integer .
> 
> By definition of D-interpretation, "xyz"^^xsd:integer has to be interpreted as a non literal. But with the constraint I just stated, the resource denoted by "xyz"^^xsd:integer must be of type xsd:integer, which, by virtue of XSD only contains integers, that are literals. Inconsistency!

Yes, I thought of that, but I don't think it works. What you get is an inconsistency in the metatheory, ie in the semantic conditions themselves, not that the graph itself is false. I mean, if the semantics says that something has to not be in LV and the semantics also says that this same thing, whatever it is, has to be in LV, then its the *semantics* which is inconsistent. What we want is that the graph should be false in every interpretation, not that the semantics should break :-)

I think allowing LV to be partial is the simplest and most intuitive way to make this work. See my most recent email to Richard. 

Pat

> 
>> 
>> We didn't do this in 2004 because the basic RDF semantic machinery
>> was seen as being defined independently of literal datatyping, but we
>> could revisit this decision, I guess. I really don't like this idea,
>> but we could do it. It would amount to incorporating datatype
>> correctness checking into the basic RDF semantic machinery, and we
>> ought to check any consequences it might have for OWL and RIF, as it
>> is a rather basic change to the design.
>> 
>> Pat
> 
> <skip>
> 
> -- 
> 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/
> 
> 

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Received on Tuesday, 13 November 2012 09:50:36 GMT

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