Re: RDF-ISSUE-79 (undefined-datatype): What is the value of a literal whose datatype IRI is not a datatype? [RDF Concepts]

Le 10/11/2011 18:43, Richard Cyganiak a écrit :
> Alex,
> On 10 Nov 2011, at 16:33, Alex Hall wrote:
>> That's almost exactly what RDF Semantics 2004 says: "Typed literals whose type is not in the datatype map of the interpretation are treated as before, i.e. as denoting some unknown thing." (Section 5.1)
> Oh, I thought I carefully read all of Section 5 but had missed that sentence. That addresses the situation indeed.
> I note the following sentence:
> [[
> The condition does not require that the URI reference in the typed literal be the same as the associated URI reference of thedatatype; this allows semantic extensions which can express identity conditions on URI references to draw appropriate conclusions.
> ]]

I do not understand this phrasing.

> So if the graph contains "xxx"^^<not-a-datatype>, then the literal might still acquire a value because<not-a-datatype>  might be owl:sameAs xsd:string, but not in any of the standard RDF entailment regimes.

In RDF or RDFS, it is not possible to say that something is not a 
datatype. Applications decide what are the datatypes in their local 
datatype map. A datatype map cannot be specified in RDF.

> So the formally correct thing to say would NOT be:
> “The value of a literal whose datatype IRI is not in the datatype map is unknown.”
> but:
> “The value of a literal whose datatype IRI does not denote a datatype in the datatype map is unknown.”

Ok but "the value" seems to indicate that, although it is not know, it 
is a value in some kind of value space (an instance of rdfs:Literal). 
But it could be a resource outside the extension of rdfs:Literal.

> Oh well.
>> I would prefer to have literals of type rdf:LangString denote themselves in all interpretations rather than some unknown thing, but I don't know how best to make it happen.  Clearly it can't be done through the L2V mechanism.
> That's easy – a new row in the first table in Section 1.4:
> If E is a language-tagged string with lexical form aaa and language tag ttt in V then I(E) =<aaa,ttt>
> and appropriate exceptions have to be stated in some places that talk about datatype IRIs – “if the datatype IRI is not rdf:langString, then …”

Yep, very good.

> Best,
> Richard

Antoine Zimmermann
ISCOD / LSTI - Institut Henri Fayol
École Nationale Supérieure des Mines de Saint-Étienne
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Received on Monday, 14 November 2011 15:19:11 UTC