Re: "do not occur"

On Jun 3, 2009, at 9:33 AM, Jonathan Rees wrote:

> On Tue, Jun 2, 2009 at 5:30 PM, Alan Ruttenberg
> <alanruttenberg@gmail.com> wrote:
>> On Tue, Jun 2, 2009 at 4:59 PM, Axel Polleres  
>> <axel.polleres@deri.org> wrote:
>>>> Incidentally, the fact that you can filter using the DATATYPE  
>>>> function
>>>> in sparql is another hint that something is amiss. By my earlier
>>>> analysis, the DATATYPE function should never return  
>>>> rdf:PlainLiteral,
>>>> according to our spec.
>>>
>>> Indeed, *according to our spec*. This is why I prefer Option 2  
>>> which makes
>>> this point clear.
>>
>> I would modify it to not try to make it invalid, but instead to make
>> it clear we say nothing about the lexical to value mapping of such
>> literals within RDF and SPARQL.
>
> In RDF, before you attempt a D-interpretation or to prove a
> D-entailment, you have to decide what D you want to use. You are
> forced to make a choice. So saying nothing isn't an option if
> rdf:PlainLiteral is in the domain of D. To implement what you suggest
> (saying nothing), the datatype map would have to be prohibited from
> having an assignment for the URI rdf:PlainLiteral, as an individual
> datatype also does not have the ability to "say nothing". If I
> understand RDF semantics correctly you would then get no entailments
> involving such typed literal nodes (loosely speaking), making them as
> ill-behaved as a literal node with a randomly selected URI after ^^
> (and I'm not sure exactly how ill-behaved that is). You could
> separately constrain interpretations by saying that the URI
> rdf:PlainLiteral must be interpreted to be the datatype described in
> section 3 of our spec; this would allow use of the URI in other
> contexts. It just wouldn't be in the datatype map.
>
> This seems really weird to me, and I haven't chased through the
> consequences to SPARQL, OWL, RIF, or anything else, so I can't
> recommend this approach.
>

Well, FWIW (not much at this stage) this is why I suggested having a  
distinct, named, semantic extension to RDF, so that there would be  
absolutely no doubt or puzzlement about what the rules were.

Pat


> Jonathan
>
>
>

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Received on Wednesday, 3 June 2009 14:46:51 UTC