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"entailment regime"?

From: Sandro Hawke <sandro@w3.org>
Date: Wed, 04 Jul 2007 10:33:40 -0400
To: public-rif-wg@w3.org
Message-ID: <32521.1183559620@ubuhebe>


(This message is likely to be controversial among the RDF folks, but I
think it's important.  It may also not be something we can agree on --
other Semantic Web working groups have been challenged by this -- but
let me at least try to make the case.)

In http://www.w3.org/2005/rules/wg/wiki/Arch/RDF, Jos writes:
> Furthermore, this data set has a particular entailment regime
> associated with it (e.g. simple, RDF, RDFS). 
>
> rif:rdfEntailmentRegime a rdf:Property ;
>     rdfs:domain rif:RuleSet ;
>     rdfs:range  rif:RDFEntailmentRegime .
    
If I understand this approach correctly, I'm afraid I have to disagree
with it.  RDF entailment regimes should *not* be specified.  It's a key
element of the architecture of the Semantic Web that semantics are
implied by the vocabulary in use, instead of being explicitely named.
This is for exactly the same reason I argued that RIF documents should
not be labeled with a dialect identifier, unless it's just a
suggestion/hint; it provides backward compatibility.  The existing
Semantic Web specifications do not provide for that explicit label, and
that omision is deliberate.

Unfortunately, the Semantic Web specifications do not say exactly how
one is supposed to infer the semantics to use, and there are some flaws
in the example set by RDFS and OWL.  I realize that's quite a
short-coming.

The idea, though, is that you use all the entailment regimes which are
defined for the vocabulary in use.  So for an RDF/XML document that uses
no RDFS or OWL terms, RDF entailment applies.  If you use RDFS terms,
RDFS entailment applies.  If you use OWL terms, OWL entailment applies.

At a high enough level, this is equivalent to just using all the
entailment regimes you can.  I know for people concerned with
theoretical properties of logics, this is painful, and it does present
some challenges.  But if there's a case where this approach is a real
problem to users, I'd like to hear about it.

(Among the flaws in the current specs, I realise, is that there are
OWL-Full entailments for a OWL-DL graph which are not OWL-DL
entailments.  That's a bug, though, and will hopefully be fixed some
day, by getting the semantics fully aligned.)

    -- Sandro
Received on Wednesday, 4 July 2007 14:34:36 GMT

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