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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: Thu, 17 Nov 2011 09:47:02 +0100
Cc: Antoine Zimmermann <antoine.zimmermann@emse.fr>, public-rdf-wg@w3.org
Message-Id: <4F5FD26B-CA84-4145-8CD4-1524A273F052@w3.org>
To: Richard Cyganiak <richard@cyganiak.de>

On Nov 16, 2011, at 22:14 , Richard Cyganiak wrote:

> Hi Ivan,
> 
> On 15 Nov 2011, at 16:59, Ivan Herman wrote:
>> 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.
> 
> They are implementation-defined, in other words, an implementation hardcodes its own datatype map.
> 
>> But that also means is that the OWL entailment that you rely on, based on owl:sameAs, may _not_ apply here.
> 
> That is possible, but I think that's beside the point.
> 
> The question was whether I can say the following in RDF Concepts: “If the IRI <bar> is not in the datatype map, then the value of any literal "xxx"^^<bar> is unknown.”
> 
> The RDF Semantics spec answers: “No you can't say that, because there might be another IRI <baz> in the datatype map that denotes the same datatype as <bar>.”
> 
> Now the built-in entailment regimes may not actually be expressive enough to say that two IRIs <bar> and <baz> denote the same datatype. And maybe not even OWL2 is expressive enough. But having that ability in *some* semantic extension of RDF might certainly be useful in a few situations, no? Are we sure that OWL3 isn't going to add an owl:equivalentDatatype property? It surely would come in handy sometimes, e.g., oracle:NVARCHAR2 owl:equivalentDatatype xsd:string.
> 
> So, the RDF Semantics answer to my question above seems to be a justified one, unless we are willing to close the door on such future semantic extensions.
> 

I understand. I think the misunderstanding or, shall we say, the uneasiness comes from the fact that if I read those lines in the current RDF document may make people think that in the current RDFS semantics that may occur. And that does not seem to be true, even with the addition of OWL 2.

We can make it more explicit, though. What about:

[[[
If the IRI <bar> is not in the datatype map, then the value of any literal "xxx"^^<bar> is unknown under the RDF Semantics.

Note: entailment systems built on top of RDF and RDF Schemas may define semantics conditions to provide an interpretation for such literals.
]]]

Cheers

Ivan

> Best,
> Richard
> 
> 
> 
>> 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/
>> mobile: +31-641044153
>> FOAF: http://www.ivan-herman.net/foaf.rdf
>> 
>> 
>> 
>> 
>> 
>> 
> 


----
Ivan Herman, W3C Semantic Web Activity Lead
Home: http://www.w3.org/People/Ivan/
mobile: +31-641044153
FOAF: http://www.ivan-herman.net/foaf.rdf
Received on Thursday, 17 November 2011 08:44:50 GMT

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