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Re: Fragments - specific proposal

From: Jim Hendler <hendler@cs.rpi.edu>
Date: Mon, 10 Dec 2007 09:25:39 -0500
Message-Id: <E0AA8A12-A1B5-4309-A134-BBCEED1A106E@cs.rpi.edu>
Cc: Ivan Herman <ivan@w3.org>, OWL Working Group WG <public-owl-wg@w3.org>
To: Carsten Lutz <clu@tcs.inf.tu-dresden.de>
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
Received on Monday, 10 December 2007 14:25:53 GMT

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