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Re: OWL2 RDF mapping and skolemization [was Re: OWL equivalentClass question]

From: David Booth <david@dbooth.org>
Date: Sun, 15 Jul 2012 23:32:16 -0400
To: Pat Hayes <phayes@ihmc.us>
Cc: Alan Ruttenberg <alanruttenberg@gmail.com>, Michael Schneider <schneid@fzi.de>, semantic-web@w3.org, nathan@webr3.org, "Peter F. Patel-Schneider" <pfpschneider@gmail.com>
Message-ID: <1342409536.2728.4115.camel@dbooth-laptop>
On Sun, 2012-07-15 at 21:48 -0500, Pat Hayes wrote:
> On Jul 15, 2012, at 9:17 PM, David Booth wrote:
[ . . . ]
> >> 
> >> But beyond that, it should always be possible to *add* information to an
> >> RDF graph that contains OWL2 encodings, and still have those encodings
> >> be recognized when mapping back from RDF to OWL2.
> 
> One has to be careful what exactly is meant by 'adding information".
> Skolemizing adds some triples but deletes some other triples (the ones
> with the bnodes in them.) They can be restored by a valid entailment,
> so in a sense the "information" is still there in the graph, but they
> are missing from the skolemized graph, and this means that said
> skolemized graph may fail to have some syntactic properties that the
> original graph had, such as being conformant to the OWL/RDF specs for
> a correct RDF encoding of some OWL. 

That sounds exactly right to me.  

So it sounds like the gap at present is that the current RDF-->OWL2
mapping rule is a little too rigid in requiring a blank node in that
position, and this forces the user to perform the (trivial) entailment
that you mention above (to add blank nodes back into the graph) if
skolemization has been performed, in order to impart the syntactic
properties that the rule expects.  This does not mean that the existing
RDF-->OWL2 mapping rule is semantically wrong, but it means that the
rule is not as user friendly as it could/should be, because it requires
the user to perform that entailment for the rule to work: essentially,
adding a corresponding bnode for every IRI in the graph.  


-- 
David Booth, Ph.D.
http://dbooth.org/

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Received on Monday, 16 July 2012 03:32:44 UTC

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