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Re: [RDF+OWL] First version OWL 2 RL embedding

From: Jos de Bruijn <debruijn@inf.unibz.it>
Date: Fri, 19 Dec 2008 10:33:30 +0100
Message-ID: <494B6A6A.7030109@inf.unibz.it>
To: Dave Reynolds <der@hplb.hpl.hp.com>
CC: RIF WG <public-rif-wg@w3.org>


Dave Reynolds wrote:
> Jos de Bruijn wrote:
>> http://www.w3.org/2005/rules/wiki/SWC#Embedding_Normalized_OWL_2_RL
>>
>> I did not yet check it thoroughly, but I think the embedding is already
>> close to a version that works.
>>
>> The embedding does not use negative guards.  Rather, it axiomatizes the
>> behavior through a number of constraints.  For example, to ensure that
>> values that are not in the value space of a particular datatype do not
>> end up in its class extension, we use formulas:
>>
>> ("a"="b" :- tr(s^^u)[rdf:type -> u']) for every well-typed literal s^^u
>> and datatype identifier u' in V such that L2V(D(u))(s) is not in the
>> value space of u'.
>>
>> This is analogous to the dt-not-type rule in Table 8 of the OWL 2 RL
>> rules in [1].
> 
> Makes sense.
> 
>> This confirms my suspicion that RDF and OWL compatibility does not
>> require negative guards.
>> As far as I'm concerned we can get rid of them.
> 
> In a theoretical but not necessarily in a practical sense.
> 
> First it would require us to only provide the translation approach to
> OWL 2 RL implementation and we would be unable to publish a static RIF
> rule set. That might be acceptable but the last discussion on this came
> to the opposite conclusion.

I was only talking from the point of view of the embedding that we need
for the RDF and OWL compatibility document, which necessarily uses the
translation approach.
I agree that for a static ruleset this might be a problem.  However,
there cannot be a single finite static ruleset, because there are lists
of various lengths, and one would need rules for each length that is in
the ontology.

> 
> Second, if I understand correctly the above approach requires NDT
> separate type checking rule for *each* literal in the ontology (where
> NDT is the number of datatypes supported). For realistic scales of
> ontology that sounds like an unrealistic number of rules.

Indeed it is.  Practical implementations would use some form of negation.

Best, Jos

> 
> Dave

-- 
Jos de Bruijn            debruijn@inf.unibz.it
+390471016224         http://www.debruijn.net/
----------------------------------------------
No one who cannot rejoice in the discovery of
his own mistakes deserves to be called a
scholar.
  - Donald Foster


Received on Friday, 19 December 2008 09:33:17 GMT

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