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

From: Richard Cyganiak <richard@cyganiak.de>
Date: Tue, 15 Nov 2011 16:15:01 +0000
Cc: public-rdf-wg@w3.org
Message-Id: <D7A5537C-A264-4CEC-923A-03C565F35C7E@cyganiak.de>
To: Antoine Zimmermann <antoine.zimmermann@emse.fr>
Hi Antoine,

On 14 Nov 2011, at 15:08, Antoine Zimmermann wrote:
>> Is it somehow possible under RDFS-Entailment + D-Entailment to get a value for "foo"^^bar if bar is not in the datatype map?
> It is not possible.

I think you're mistaken.

if <bar> owl:sameAs <baz>, and <baz> is an IRI in the datatype map, then "foo"^^<bar> may have a well-defined value even if the IRI <bar> is not in the datatype map.

On 14 Nov 2011, at 15:18, Antoine Zimmermann wrote:
>> 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.

It speaks to the example above: The IRI in the typed literal may be <bar>, and the IRI in the datatype map may be <baz>, and we may know through an owl:sameAs statement that <bar> and <baz> denote the same datatype. In other words, the datatype denoted by <bar> might be in the range of the datatype map even though <bar> is not in the domain of the datatype (but <baz> is).

>> 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.

Of course. The point was that <not-a-datatype> is an IRI that is not in the application's datatype map.

>> 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). 

That just seems to be an unsound inference.

A “value space” in RDF Concepts is a part of a “datatype”. We have just established that we are talking about literals “whose datatype IRI does not denote a datatype”. So there is no basis for inferring that the value of such a literal must be “in some kind of value space”.

And regarding rdfs:Literal: From the statement “the value of X is unknown” you cannot reasonably infer the statement “the value of X is a member of rdfs:Literal”. I can see no basis whatsoever for that inference.

Received on Tuesday, 15 November 2011 16:15:41 UTC

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