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Re: ISSUE-131 (OWL R Unification): Fundamental understanding problems

From: Ian Horrocks <ian.horrocks@comlab.ox.ac.uk>
Date: Mon, 11 Aug 2008 20:18:35 +0100
Message-Id: <9F81ED49-1247-4643-A449-4492BF900383@comlab.ox.ac.uk>
Cc: Michael Schneider <schneid@fzi.de>, "public-owl-wg Group WG" <public-owl-wg@w3.org>
To: Jim Hendler <hendler@cs.rpi.edu>


It is true that some details, particularly those related to  
conformance, still need to be precisely specified, but it seems to me  
that the unification proposal makes everything much less confused:  
there would be just one rules profile (now called OWL-RL), and it  
would behave in pretty much the way you describe below. In  
particular, the unification proposal is designed to *avoid* the  
craziness of a third semantics, which is exactly what we would have  
if we left things as they are.


On 8 Aug 2008, at 17:42, Jim Hendler wrote:

> Having left the WG, I seem to still be being pulled in a lot by  
> side emails, so let me state, as RPI AC rep, that we agree with  
> Michael that as yet this is not specified to the point where we  
> know for sure what it means, but given the spirit of the initial  
> emails, we are troubled.  The reasons were well stated by Ivan.  It  
> seems to me that this WG is going to great lengths to sow confusion  
> between a simple meaning of DL vs. Full, instead of the relatively  
> straightforward way it was resolved in the first WG.  Roughly  
> speaking, we would like to see a solution where the rules, applied  
> to an OWL DL ontology would produce and OWL DL ontology (thus OWL R  
> would be "DL compliant" whatever that means) and that a "full  
> implementation of OWL R DL" would be expected to match the DL  
> semantics.  We would expect that the same set of rules, applied to  
> an OWL Full ontology (defined at the moment as something that  
> includes some feature outside OWL DL) would do the same -- i.e.  
> would produce a new ontology not expected to be in OWL DL and if it  
> didn't include all the expected inferences, as defined by the  
> rules, it would not be considered a "full implementation of OWL R"  
> -- I don't understand this craziness about needing a third  
> semantics, nor do I understand why OWL R is not just OWL R.
>  Frankly, this WG seems very confused as to what OWL DL and Full  
> should/could be, and I think the proposals with respect to the  
> renaming, the addition of odd triples, and this so-called  
> unification will make this confusion even worse.
>   -Jim H.
> On Aug 7, 2008, at 8:23 PM, Michael Schneider wrote:
>> Dear all,
>> in spite of a lot of discussion, which has happened on the  
>> unification
>> issue, both in the mailing list and at meetings, and additional  
>> discussions
>> which I had privately with WG members, I stronger than ever have  
>> the feeling
>> that I do not understand what the unification will actually look  
>> like in the
>> end. So I would like to hear from other WG members what they  
>> believe will be
>> the result.
>> Below, I have assembled a list of assumptions, which represent my  
>> current
>> understanding. These points can, in the simplest case, be answered  
>> with
>> "yes" or "no". But in the case of "no", I would appreciate to hear  
>> from you
>> what your understanding is instead.
>> Please keep in mind that I am really only interested in  
>> understanding how
>> exactly OWL R will be specified in the end. This means,  
>> essentially, that I
>> want to know what the syntax and what the precise semantics of OWL  
>> R will
>> be, and also, what the exact role of the OWL R ruleset will be for  
>> OWL R.
>> (On the other hand, I am *not* interested in, for example, the  
>> question when
>> may or should an OWL R reasoner signal a warning to a user, since  
>> such an
>> implementation-specific behavior is completely outside the formal
>> specification of a language.)
>> Here is the list of my current assumptions:
>> (A) The "syntactic fragment" of the unified OWL R language will be  
>> defined
>> by today's syntax of OWL R DL, as specified in sec 4.2 of the  
>> Profiles
>> document. An ontology will be called a "valid OWL R ontology", if  
>> it matches
>> these syntactic restrictions.
>> (B) Nothing specific is said about ontologies which do not fall in  
>> this
>> syntactic fragment, so an OWL R compliant reasoner is free to  
>> either deny or
>> accept such an ontology as syntactically valid input.
>> (C) For ontologies matching the syntactic fragment, the OWL R  
>> semantics of
>> such an ontology will be specified in parallel by the OWL DL  
>> semantics (as
>> it is nowadays true for OWL R DL), and also w.r.t. the ruleset of  
>> today's
>> OWL R Full.
>> (D) For (C) to make sense, the DL semantics and the rule based  
>> semantics
>> have to be exactly equivalent for ontologies matching the syntactic
>> fragment. It is believed that this relationship holds. For ontologies
>> outside the syntactic fragments, this equivalence is *not*  
>> required to hold.
>> (E) For ontologies outside the syntactic fragment, the only semantic
>> restriction on reasoners is that they must not produce inferences  
>> which go
>> beyond OWL Full (without "R"!) entailment. So they may produce  
>> whatever
>> inferences they like, as long as they keep being in the scope of  
>> OWL Full.
>> In particular, they MAY produce all or only some of the inferences  
>> which can
>> be derived from the OWL R ruleset for such ontologies, but this  
>> will in no
>> way be enforced by the specification or OWL R.
>> Regards,
>> Michael
>> --
>> Dipl.-Inform. Michael Schneider
>> FZI Forschungszentrum Informatik Karlsruhe
>> Abtl. Information Process Engineering (IPE)
>> Tel  : +49-721-9654-726
>> Fax  : +49-721-9654-727
>> Email: Michael.Schneider@fzi.de
>> Web  : http://www.fzi.de/ipe/eng/mitarbeiter.php?id=555
>> FZI Forschungszentrum Informatik an der Universität Karlsruhe
>> Haid-und-Neu-Str. 10-14, D-76131 Karlsruhe
>> Tel.: +49-721-9654-0, Fax: +49-721-9654-959
>> Stiftung des bürgerlichen Rechts
>> Az: 14-0563.1 Regierungspräsidium Karlsruhe
>> Vorstand: Rüdiger Dillmann, Michael Flor, Jivka Ovtcharova, Rudi  
>> Studer
>> Vorsitzender des Kuratoriums: Ministerialdirigent Günther Leßnerkraus
> "If we knew what we were doing, it wouldn't be called research,  
> would it?." - Albert Einstein
> Prof James Hendler				http://www.cs.rpi.edu/~hendler
> Tetherless World Constellation Chair
> Computer Science Dept
> Rensselaer Polytechnic Institute, Troy NY 12180
Received on Tuesday, 12 August 2008 08:39:44 UTC

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