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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: Ivan Herman <ivan@w3.org>
Date: Tue, 15 Nov 2011 17:59:47 +0100
Cc: Antoine Zimmermann <antoine.zimmermann@emse.fr>, public-rdf-wg@w3.org
Message-Id: <CD2E55C0-5CC1-495B-8633-9C128ECBDBFD@w3.org>
To: Richard Cyganiak <richard@cyganiak.de>
Richard,

to be honest I am not completely sure you are right, but I am on a slightly slippery slope here myself.

To quote from the OWL spec (but that is probably true for the RDFS spec, too, the OWL spec seems to be clearer to me in this respect):

[[[
A set of datatypes supported by a reasoner is called a datatype map. This is not a syntactic construct — that is, it is not used directly to construct OWL 2 ontologies in a way that, say, classes and datatypes are. Because of that, a datatype map is not represented in the structural specification of OWL 2.
]]] http://www.w3.org/TR/owl2-syntax/#Datatype_Maps

The way I, naïvely, interpret this is that the datatypes maps, their definition, the way the various mappings are associated with a URI, etc, are outside the OWL or RDFS spec. But that also means is that the OWL entailment that you rely on, based on owl:sameAs, may _not_ apply here. After all, owl:sameAs is not some sort of a universal magic that blurs the differentiation of URI-s, it has, instead, some entailment rules associated to it. (Eg, Table 4 of [1]). Ie, I am not sure that it follows, in OWL, that the URI <bar>, in your original example, is properly associated to datatype map LV's, just because it is owl:sameAs to <baz> and the <baz> is indeed associated with a datatype mapping.

Again, I am not an expert here, and I know I do some hand-waiving. If this is really important, we should ask somebody who really know these things, like Boris Motik.

Ivan

[1] http://www.w3.org/TR/owl2-profiles/#Reasoning_in_OWL_2_RL_and_RDF_Graphs_using_Rules


On Nov 15, 2011, at 17:39 , Richard Cyganiak wrote:

> On 15 Nov 2011, at 16:30, Ivan Herman 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.
>> 
>> Just to play the disagreeable guy: owl:sameAs is not an RDFS term. If we are talking about RDFS-Entailment, this will not work...
> 
> Ok, you're right Ivan, under RDFS-Entailment "foo"^^<bar> won't have a well-defined value.
> 
> But to quote again the phrase from Section 5.1 that I quoted earlier:
> 
> [[
> The condition does not require that the URI reference in the typed literal be the same as the associated URI reference of the datatype; this allows semantic extensions which can express identity conditions on URI references to draw appropriate conclusions.
> ]]
> 
> My original question was: Is it true that "foo"^^<bar> has an L2V-assigned value if and only if <bar> is in the domain of the datatype map? The answer to that is: “There might be entailment regimes where it's not true, OWL's RDF-based semantics being an example.”
> 
> Best,
> Richard


----
Ivan Herman, W3C Semantic Web Activity Lead
Home: http://www.w3.org/People/Ivan/
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FOAF: http://www.ivan-herman.net/foaf.rdf
Received on Tuesday, 15 November 2011 16:57:12 GMT

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