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Re: Fragments - specific proposal

From: Carsten Lutz <clu@tcs.inf.tu-dresden.de>
Date: Mon, 10 Dec 2007 16:25:05 +0100 (CET)
To: Jim Hendler <hendler@cs.rpi.edu>
Cc: Ivan Herman <ivan@w3.org>, OWL Working Group WG <public-owl-wg@w3.org>
Message-id: <Pine.LNX.4.64.0712101621171.3986@frege.inf.tu-dresden.de>

I feel I am repeating myself, but: I have only said that the tractable
fragment (whether "fragment" is meant syntactically or semantically I
don't care) that you have mentioned was not clearly specified. Below
you say that your fragment "can fall into polynomial with certain
restrictions" and "those restrictions are what would need design".

This *is* *not* clearly specified. No big problem, as you still have
enough opportunity to do it. That's all I said. I didn't say anything
about semantics. Please don't cite me wrongly.

greetings,
 		Carsten

On Mon, 10 Dec 2007, Jim Hendler wrote:
>
> I did indeed refer to that page - the language features I outlined clearly 
> can fall into polynomial with certain restrictions (in fact, they are all 
> doable in various datalog and Horn subset)  - those restrictions are what 
> would need design - in the sense that the unrestricted use of the feature set 
> (including the ability to redefine the features in RDF) would clearly be 
> undecidable - the question is can the restrictions be specified simply 
> enough.
>
> btw, let me be clear to the some of the assembled, you talk about semantics 
> as if there is only one such thing - I point out that the world include 
> programming language semantics, operationally defined semantics, database 
> semantics, axiomatic semantics and many other things beyond model theory.  I 
> am perfectlt content for the langauge to only specify an operational 
> semantics normatively, and then let researchers determine the formal 
> model-theoretic semantics.  So when you or Peter says the language is not 
> defined, you are wrong, it is carefully designed against the operational 
> semantics clearly specified in the OWL 1.0 documents.  Since I defined it as 
> an OWL Full subset, I would point out that it is also formally defined 
> through the OWL Full (RDFS) semantics.
>
> To reach consensus, I've expressed a willingness to see us work on a more 
> formal semantics for a restricted subset of this.  FWIW, I'd personally be 
> happier seeing us just define this as a named subset of OWL Full w/o proof of 
> complexity or model-theory, it was my feeling from the WG f2f minutes and 
> parts I heard, that some in the group could not live with it.
>
> But just so we're totally clear - the RDFS 3.0 that I proposed is a fully 
> defined language with all the semantics it needs (from the OWL 1.0 and RDF 
> documents) - so please don't say I haven't defined the language.
> -JH
>
>
> On Dec 10, 2007, at 6:00 AM, Carsten Lutz wrote:
>
>> On Mon, 10 Dec 2007, Ivan Herman wrote:
>>> 
>>> Carsten Lutz wrote:
>>>> 
>>>> Hi Jim,
>>>> 
>>>> On Fri, 7 Dec 2007, Jim Hendler wrote:
>>>> 
>>>>> 2 - RDFS 3.0
>>>>> I propose we name a subset called RDFS 3.0 which is less than OWL Lite
>>>>> - aimed primarily at universals - i.e. named classes and properties,
>>>>> no restriction statements involved.
>>>>> There should be a version of this which is provably polynomial within
>>>>> certain restrictions (at least no redefinition of the language
>>>>> features, possibly
>>>> 
>>>> Then it would IMHO be appropriate if some of the supporters of RDFS
>>>> 3.0 would state precisely what this tractable fragment is and prove
>>>> that it is tractable. Otherwise, I feel I am discussing a ghost.
>>>> 
>>> 
>>> I think Jim refers to:
>>> 
>>> http://www.w3.org/2007/OWL/wiki/Fragments
>>> 
>>> which posted some times ago.
>> 
>> Thanks, I know that page. But to me Jim's remark doesn't sound as if
>> referring to that page.  He says that "There should be a version of
>> this which is provably polynomial". Since I think that polynomiality
>> is a very important property for fragments of OWL, I would like to
>> understand what precisely that version is. Is it the one on the page
>> you refer to? If not, what exactly does it look like?
>> 
>> greetings,
>> 		Carsten
>> 
>> --
>> *      Carsten Lutz, Institut f"ur Theoretische Informatik, TU Dresden 
>> *
>> *     Office phone:++49 351 46339171   mailto:lutz@tcs.inf.tu-dresden.de 
>> *
>
> "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
>
>
>
>

--
*      Carsten Lutz, Institut f"ur Theoretische Informatik, TU Dresden       *
*     Office phone:++49 351 46339171   mailto:lutz@tcs.inf.tu-dresden.de     *
Received on Monday, 10 December 2007 15:25:26 GMT

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