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

Hi Richard,

Le 15/11/2011 17:15, Richard Cyganiak a écrit :
> 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.

Assuming that owl:sameAs was in the RDF/RDFS spec, this even would not
make "foo"^^<bar> be interpreted identically as "foo"^^<baz>. The 
interpretation of typed literals is not influenced by anything in the 
ontology, even in OWL. "foo"^^<bar> is always interpreted as 
L2V(D(<bar>))("foo") according to the datatype map D.

FYI, look at section 4.2 of the OWL 2 RDF-based semantics:

"IL is a mapping from typed literals "s"^^u in V to their denotations in 
IR, where IL("s"^^u) = L2V(d)(s), provided that d is a datatype of D, 
IS(u) = d, and s is in the lexical space LS(d); otherwise IL("s"^^u) is 
not in LV."

So the interpretation of "s"^^u (or "foo"^^<bar>) is in the value space 
of <bar> if and only if <bar> is in the datatype map AND "foo" is in the 
lexical space of D(<bar>). Otherwise it is not in LV (or, I would say, 
it is not a "value").

> 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.

I'm just saying that the word "value" may be misunderstood. For 
instance, I would not consider a person to be a value. But 
"foo"^^<not-a-datatype> may denote a person or anything.

> Best, Richard

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
Fax:+33(0)4 77 42 66 66

Received on Tuesday, 15 November 2011 21:24:27 UTC