W3C home > Mailing lists > Public > public-rdf-wg@w3.org > November 2011

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: Wed, 16 Nov 2011 21:14:06 +0000
Cc: Antoine Zimmermann <antoine.zimmermann@emse.fr>, public-rdf-wg@w3.org
Message-Id: <6A6E744C-719D-4923-88E5-EA0CEDF1C638@cyganiak.de>
To: Ivan Herman <ivan@w3.org>
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.

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
> 
> 
> 
> 
> 
> 
Received on Wednesday, 16 November 2011 21:14:41 GMT

This archive was generated by hypermail 2.3.1 : Tuesday, 26 March 2013 16:25:46 GMT