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Re: Fragments - specific proposal

From: Jim Hendler <hendler@cs.rpi.edu>
Date: Mon, 10 Dec 2007 10:55:47 -0500
Message-Id: <75342EAE-B065-4537-A9AD-F40814506347@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>

On Dec 10, 2007, at 10:25 AM, Carsten Lutz wrote:

> 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.

the whole purpose of the WG is to specify the languages we endorse,  
very rare that one endorses some existing thing - just as I proposed  
that OWL Lite could look a lot like EL++ - with some changes (I'm  
thinking mainly of instance stuff which shouldn't effect  
polynomiality)  so too could RDFS be ammended - but I don't see it as  
my job to prove things that I don't care at all about.
  -JH
p.s. btw, polynomial with respect to what algorithmically?



>
> 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     *

"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 15:56:05 GMT

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