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Re: ISSUE: OWL-DL compatibility

From: Jos de Bruijn <debruijn@inf.unibz.it>
Date: Wed, 11 Nov 2009 00:11:12 +0100
Message-Id: <D5484690-DB19-4103-A7EF-25FCF3159FE6@inf.unibz.it>
To: Chris Welty <cawelty@gmail.com>
Cc: "kifer@cs.sunysb.edu" <kifer@cs.sunysb.edu>, RIF WG Public list <public-rif-wg@w3.org>
I am willing to make both changes.

Cheers, Jos

On 10 Nov 2009, at 23:59, Chris Welty <cawelty@gmail.com> wrote:

>
> Unless anyone else has an opinion, Jos are you willing to make that  
> change?
>
> On a different but related note, Ian Horrocks posted a public  
> comment that the new terminology for that-formerly-known-as-OWL-DL  
> is "OWL Direct Semantics", and for that-formerly-known-as-OWL-Full  
> is "OWL RDF-based Semantics" (see [http://lists.w3.org/Archives/Public/public-rif-comments/2009Nov/0001.html] 
> )
>
> I think a quick fix would be to replace "OWL Full" with "OWL RDF- 
> based Semantics" and replace "OWL-DL" with "OWL Direct Semantics".   
> This isn't precisely correct in general, but I think based on the  
> way we use the difference (between OWL Full and OWL DL), it works.
>
> This doesn't change anything fundamental so its clearly just a bug  
> fix, if you are willing to make the change.  Are you?
>
> -Chris
>
>
> Michael Kifer wrote:
>> 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
>>>>>
>
> -- 
> Dr. Christopher A. Welty                    IBM Watson Research Center
> +1.914.784.7055                             19 Skyline Dr.
> cawelty@gmail.com                           Hawthorne, NY 10532
> http://www.research.ibm.com/people/w/welty
Received on Tuesday, 10 November 2009 23:11:59 GMT

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