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Re: ISSUE: OWL-DL compatibility

From: Michael Kifer <kifer@cs.sunysb.edu>
Date: Tue, 10 Nov 2009 14:48:27 -0500
To: Chris Welty <cawelty@gmail.com>
Cc: Jos de Bruijn <debruijn@inf.unibz.it>, RIF WG Public list <public-rif-wg@w3.org>
Message-ID: <20091110144827.4b8335df@kiferdesk>
Yes, I agree that 3a is a reasonable fix. 3b is too big of a change, and I was
not suggesting it for this round.

michael


On Tue, 10 Nov 2009 10:53:32 -0500
Chris Welty <cawelty@gmail.com> wrote:

> 
> I read this a little more carefully.
> 
> Basically, the issue is whether to add some correspondence between rif:subclass 
> and rdf:subclass and between rif:type and rdf:type *in the OWL compatibility 
> section* of SWC.  Such a correspondence is already there for RDF compatibility, 
> but Michael noted that it is not "inherited" by the "OWL-DL" (now know as OWL 
> Direct Semantics) section.  So, currently in SWC, the OWL-DL compatibility has 
> no correspondence between the rather obvious type/subclass relations in the two 
> languages.
> 
> I agree this is a problem and should be fixed, and option #1 in Michael's 
> analysis, copied below (to leave it as is) is unacceptable.
> 
> Option #2 is to just add a sentence to the text saying there is no 
> correspondence between owl and rif type/subclass.  This is less than satisfactory.
> 
> Option #3 is to "fix" it somehow, and there are two variations there, I'll call 
> them 3a (just repeat the correspondences from RDFS in OWL-DL) and 3b (do the 
> best possible job mapping between owl and rif subclass).
> 
> </chair>I prefer option 3a.  I agree with Jos' analysis of option 3b and think 
> it is too big a change.<chair>
> 
> As chair, I am also willing to accept 2 or 3a as an oversight and bug fix (I 
> personally thought the correspondence between type and subclass were "inherited" 
> from the RDF correspondence, so 3a would just make it the way I thought it was), 
> however 3b seems to me, procedurally, to be much more significant and requires a 
> new last call for SWC.
> 
> -Chris
> 
> Jos de Bruijn wrote:
> >> In today's telecon I was asked to reanimate the issue of OWL compatibility,
> >> which was discussed 1 month ago.
> >>
> >> Here is the relevant message:
> >>
> >> http://lists.w3.org/Archives/Public/public-rif-wg/2009Sep/0017.html
> >>
> >> The current situation is a bug, IMO. If it isn't a bug then at least that part
> >> of the document is very unsatisfactory and obscure. Jos proposed 3 solutions:
> >>
> >> 1- leave things as they are, assuming that # and ## are not of interest
> >>    to users of RIF-OWL DL combinations
> >> 2- explain the use of # and ## in the document (this would certainly not
> >>    be a substantive change, so we should not run into procedural problems)
> >> 3- define the semantics of # and ## in RIF-OWL DL combinations in a
> >>    similar fashion as in RIF-RDF combinations: a one-to-one correspondence
> >>    between # and OWL class membership statements and implication between ##
> >>    and OWL subclassing.
> >>
> >> The easiest for him would be to do nothing (1), thus leaving things
> >> unsatisfactory and obscure. His next choice is (3), which is also my choice and
> >> the "right thing to do."  (3) stretches things a little, but it can be argued
> >> that it is a simple fix.
> > 
> > In my earlier e-mail to Michael referred to I did not say what my
> > preference is among the mentioned options.  I guess arguments can be
> > made for all three options, so in fact I do not have a strong
> > preference, but I do have a concern about option (3): implementation
> > might be harder.  If, for example, implementation is done through
> > embedding in other rules system, like the embedding of RIF-OWL2RL
> > combination in the appendix of the document, quite a few rules need to
> > be added for the ## construct.
> > In particular, for every pair of distinct class names (A,B), we need to
> > add the rule:
> > 
> > Forall ?x (?x[rdf:type -> B] :- And(?x[rdf:type -> A] A##B))
> > 
> > This means adding a quadratic number of rules.
> > 
> > Dealing with # is easy: in the mapping of RIF DL-document formulas to
> > RIF documents [1] we simply map a#b to tr'(b)(a). Clearly, we would
> > restrict b in formulas a#b to constant symbols.
> > 
> > 
> > [1]
> > http://www.w3.org/TR/rif-rdf-owl/#Embedding_RIF_DL-document_formulas_into_RIF_BLD
> > 
> > 
> >> Solution (2) is more work. It fixes the obscurity aspect, not the
> >> unsatisfactory aspect of the definitions. So, (3) seems like the best way to
> >> proceed.
> >>
> >> Solution (3) still leaves some problems, which are unrelated to the above
> >> issues. In the current semantics, subclassing in RIF implies subclassing in
> >> OWL/RDF, but not vice versa.
> >>
> >> In this regard, I would like to point to my follow-up message
> >> http://lists.w3.org/Archives/Public/public-rif-wg/2009Sep/0019.html
> >> Here I proposed a stronger semantics, which fixes this non-entailment problem.
> > 
> > Michael proposed the following semantics:
> > 
> > {(A,B) | A rdfs:subclassOf B and A != B on the RDF side}
> >                 = {(A,B) | A##B on the RIF side}
> > 
> > I feel that this would take us out of Horn, even when considering Simple
> > entailment, because implementation would require (classical) negation.
> > At least, that is the only way I current see how this could be
> > implemented. As we know, classical negation in the body amounts to
> > disjunction in the head, so we would end up adding the following rule to
> > the embedding of RDF-RDF combinations:
> > 
> > Forall ?x, ?y (Or(?x##?y ?x=?y) :- ?x[rdfs:subClassOf -> ?y])
> > 
> > For RIF-OWL DL combinations such a semantics is even more problematic,
> > because subclass in OWL DL means subset relation between class
> > extensions, so the condition would look something like (X^C is the class
> > extension of X):
> > 
> > {(A,B) | A^C subset B^C and A^C != B^C on the RDF side}
> >                 = {(A,B) | A##B on the RIF side}
> > 
> > (Actually, we will need to apply some tricks here, since A and B are not
> > constants on the OWL side, but I guess we can come up with a definition
> > that kind-of achieves this semantics)
> > 
> > A formula implementing the => direction of the condition for a pair of
> > class names A,B would look something like (again, negation in the body
> > becomes disjunction in the head):
> > 
> > Forall ?x (
> >   Or(A##B
> >      And(Forall ?x(?x[rdf:type -> B] :- ?x[rdf:type -> A])
> >          Forall ?x(?x[rdf:type -> A] :- ?x[rdf:type -> B])))
> >   :-
> >   Forall ?x(?x[rdf:type -> B] :- ?x[rdf:type -> A]))
> > 
> > 
> > So, I would not be in favor of extending either the semantics of RDF or
> > the semantics of OWL DL combinations with such a condition.
> > 
> > 
> > Best, Jos
> >> This would certainly be a substantive change semantically (although not
> >> significant textually). If we don't have the energy to do it this time,
> >> maybe for RIF 1.1.
> >>
> >> michael
> >>
> > 
> 
Received on Tuesday, 10 November 2009 19:49:02 GMT

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