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RE: OWL Full proposal (sort of) - addressing my Action

From: Michael Schneider <schneid@fzi.de>
Date: Wed, 13 Feb 2008 12:03:22 +0100
Message-ID: <0EF30CAA69519C4CB91D01481AEA06A0750B70@judith.fzi.de>
To: "Ian Horrocks" <ian.horrocks@comlab.ox.ac.uk>, "Jim Hendler" <hendler@cs.rpi.edu>
Cc: "Web Ontology Language ((OWL)) Working Group WG" <public-owl-wg@w3.org>, "Ivan Herman" <ivan@w3.org>, "Jeremy Carroll" <jjc@hpl.hp.com>
Hi Ian and Jim!

(Ok, this might become a bit controversal, but let's see... :))

Maybe there is an option, which might work, and which has precedence. Ivan came up with an interesting point last week [1]. He stated that the RDF semantics spec [2] 

    "includes a bunch of entailment rules which are 
    the type of axiomatic rules that you [Jim] refer to". 

I think this is a relevant observation.

As I wrote in [3], the OWL-Full semantics are actually specified as a set of model-theoretic "semantic conditions". And I believe that it really is appropriate to /specify/ the OWL-Full semantics for the different language features in this way. When I have a QCR described by a set of RDF triples, then defining the meaning of this collection of triples by set theoretical means is clear and straightforward, IMO. And I think this also eases the task of making OWL-Full "downwards" compatible with OWL-DL, since one can try to "borrow a little bit" from those specifications which already exist in the DL semantics document. :) Anyway, doing it this way will give us the desirable rigour.

On the other hand, I believe that the semantic conditions often do not very well show how OWL-Full "works", or how parts of it can be implemented. Much better is this captured, IMHO, by "triple entailment rules". By this I mean rules, which get a few RDF triples as their input, and fire a few new RDF triples as their output, e.g.:

    IF (?x rdfs:subClassOf ?y) AND (?y rdfs:subClassOf ?z) 
    THEN (?x rdfs:subClassOf ?z)

The "meaning" of a given RDF graph can then be understood to be the inference graph, which consists of the original triples, and all those triples which are additionally entailed by all triple entailment rules.

Semantic conditions do not have such a triple-to-triple form, and for the example above doesn't even exist a semantic condition which could be regarded to be the "direct model-theoretic analogon". However, it isn't hard to see that from OWL-Full semantics the above triple entailment rule can be "derived" (in some sense).

The RDF(S) semantics spec [2] contains a section which itemizes a set of such triple entailment rules [4]. This is an /informative/ section, while the sections which introduce the semantic conditions are normative. If I had to point someone to a resource where he can learn how OWL-Full "works", I think I would rather point him to this collection of triple entailment rules.

Regrettably, there is no such collection of triple entailment rules in the OWL-1.0-Full spec. I would think that having such a collection would be a win, and I expect the costs for its creation to be mediocre. Perhaps, such a collection doesn't even have to be complete, if this is possible at all. But even a "proper selection" would already be of value, I suppose. 

Such an informative section which itemizes triple entailment rules should probably not be part of the UFDs, since it would still be very technical. Of course, one could have a few of these rules in a Primer document as examples for explaining OWL-Full, and then point to the respective section in the Full semantics spec as a reference. 

Btw: The above example of a triple entailment rule does not just accidentally look similar to a Jena rule [5]. :) AFAIU, the Jena inference support actually follows the triple entailment rule approach as given in [4], see [6].


[1] <http://lists.w3.org/Archives/Public/public-owl-wg/2008Feb/0051.html>
[2] <http://www.w3.org/TR/rdf-mt/>
[3] <http://lists.w3.org/Archives/Public/public-owl-wg/2008Feb/0068.html>
[4] <http://www.w3.org/TR/rdf-mt/#rules>
[5] <http://jena.sourceforge.net/inference/index.html#rules>
[6] <http://jena.sourceforge.net/inference/index.html#RDFSintro>

>-----Original Message-----
>From: public-owl-wg-request@w3.org 
>[mailto:public-owl-wg-request@w3.org] On Behalf Of Ian Horrocks
>Sent: Tuesday, February 12, 2008 7:09 PM
>To: Jeremy Carroll
>Cc: Jim Hendler; Web Ontology Language ((OWL)) Working Group WG
>Subject: Re: OWL Full proposal (sort of) - addressing my Action
>I share Jeremy's desire to maintain a significant degree of rigour  
>w.r.t. OWL Full; in fact I would say the same for all species/ 
>fragments/conformance-levels. Moreover, from what Jim says in emails  
>such as [1] it would seem that he has no objection to this and  
>perhaps even believes it to be mandatory. Instead, what he seems to  
>be asking for (in [1] at least) is a more human readable explanation  
>for those who find model theories difficult to understand. I don't  
>see any problem with that -- in fact we already have a commitment to  
>producing such documents and even a UFDTF busily engaged in their  
>development. So, if we were to agree to produce a "delta to OWL-1.0- 
>Full" as outlined by Michael in [2] plus suitable documentation for  
>the MT-challenged, would this satisfy everyone's requirements?
>[1] http://lists.w3.org/Archives/Public/public-owl-wg/2008Feb/0069.html
>[2] http://lists.w3.org/Archives/Public/public-owl-wg/2008Feb/0068.html

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
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Received on Wednesday, 13 February 2008 11:04:10 UTC

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