Re: AW: AW: {Disarmed} Re: blank nodes (once again)

On Mar 24, 2011, at 11:17 AM, Sandro Hawke wrote:

> On Thu, 2011-03-24 at 16:07 +0000, Michael Schneider wrote:
>> Hi Sandro!
>> Sandro Hawke wrote:
>>> Is there something in the OWL specs that says OWL doesn't work 
>>> (or that we're no longer in DL) if the nodes composing the lists 
>>> are not blank? That would be a problem.
>> In the OWL 2 Mapping to RDF Graphs at
>>    <>
>> many of the RDF graph patterns on the left-hand-side of inverse mapping rules from RDF to the Functional Syntax are only defined for blank nodes. See, for instance, Table 16, where you can see the differences: there are some rules that use a string "*:x", which stands for an IRI according to the definition in Chap 1, some rules which can be used with both IRIs and blank nodes, as denoted by the string "x", and some of the rules in that table are really only defined for blank nodes only, denoted by string "_:x". You can find many more examples for blank node-only rules in the other tables. 
>> Specifically for lists, their inverse mapping is treated by Table 3, which only handles the case of blank nodes.
>> OWL 2 DL parsers may, of course, decide to relax on this and also parse structures having URIs instead of blank nodes. But, strictly speaking, such RDF graphs do not count as valid OWL 2 DL ontologies in RDF graph form. 
> Well, that's annoying.   Do you know of a technical reason for doing it
> this way, or was it just that no one saw a reason to allow nonblank
> nodes?  

The reason was so that RDF inference would not affect the OWL syntax. 

>   Sigh.   I guess it's a small problem compared to the related
> problem that (as I recall) people can't even use RDF Lists for data in
> OWL DL.     *Even Bigger Sigh*.
> I guess the important question: is OWL 2 Full okay with people
> Skolemizing the ontology?

The answer is, Yes OK to skolemize your content. No, not OK to skolemize the RDF encoding of the OWL syntax, including the RDF collections (lists). So this change would not be a zero-cost painless change for OWL. But it would be fairly easy to modify the specs the new RDF; and all the pain is in the specs: for implementors, the change would be easy, possibly no change at all (depending on how they deal with RDF collections.) 


>    -- Sandro

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Received on Thursday, 24 March 2011 17:33:01 UTC