W3C home > Mailing lists > Public > public-rif-wg@w3.org > February 2008

Re: RIF RDF and OWL compatibility - mini review

From: Dave Reynolds <der@hplb.hpl.hp.com>
Date: Mon, 18 Feb 2008 17:31:59 +0000
Message-ID: <47B9C10F.5000508@hplb.hpl.hp.com>
To: Jos de Bruijn <debruijn@inf.unibz.it>
CC: RIF WG <public-rif-wg@w3.org>

Hi Jos,

>> I don't see how the fix up of constraining the truth valuation so that 
>> the frame and non-frame representations are equivalent works. In BLD 
>> predicates and constants are required to be disjoint so I don't see 
>> how the constraints like:
>>   It-dl( t [ rdf:type -> A] ) = IR(A)(t)
>> can be applied.
> 
> These are not constraints, but definitions.  Effectively, they make 
> frames just another way of writing unary and binary predicates.

Yes though with the well-formedness restrictions in BLD you can only 
write them one way or the other, you can't mix and match, right?

>> Either this is a pure syntactic preprocessing step (in which case case 
>> define it as such, instead of via semantic fix up) or you are lifting 
>> that restriction in the BLD semantics.
> 
> It could have been defined as a syntactic preprocessing step (rewriting 
> frames to unary and binary predicates); this is explained just above 
> section 4.3.2.1.  However, I find the current definition more elegant, 
> because it provides a direct semantics, rather than requiring two steps 
> (rewriting and interpretation).

A plausible argument, I'll have to let it sink in.

>> In that case why not use that for RDF and OWL FULL as well?
> 
> It would disallow quantification over classes and properties, i.e., no 
> variables are allowed to occur in class or property positions. I believe 
> that such a restriction is unacceptable for RDF-rules.  Plus, it is 
> unclear to me what the consequences would be of using equality in the 
> rules in such a setting.

I was thinking that you must have lifted the disjointness constraints on 
BLD in which case one could write in frame form when you want such 
quantification and in predicate form when you didn't. Without lifting 
those restrictions I can see that you can only write in one form or the 
other in which case you are are right, the predicate form *on its own* 
is not sufficient for RDF.

Dave
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Received on Monday, 18 February 2008 17:32:45 GMT

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