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Re: Fragments - specific proposal

From: Carsten Lutz <clu@tcs.inf.tu-dresden.de>
Date: Sat, 08 Dec 2007 10:59:52 +0100 (CET)
To: Jim Hendler <hendler@cs.rpi.edu>
Cc: OWL Working Group WG <public-owl-wg@w3.org>
Message-id: <Pine.LNX.4.64.0712081041540.12882@frege.inf.tu-dresden.de>

Hi Jim,

On Fri, 7 Dec 2007, Jim Hendler wrote:
> In light of the conversations and presentation at the f2f as best I could 
> follow - I propose the following which I believe is actually within the 
> spirit of consensus

I strongly disagree. You are addressing here the issues of

1. whether there should be an official OWL Light
2. whether there should be one or several OWL Lights
3. what precisely it/they will be.

Based on the discussions at and around the meeting, I think it is fair
to say that all these issues are highly controversial. My impression is
not at all that what you propose is in the spirit of consensus.

> Summary (details below)  I propose we redefine OWL Lite to be somewhat less 
> than is currently in the language, that we name a new subset with the intent 
> of adding just enough OWL to RDFS to match current "low end" needs, and I 
> propose that we create an easily findable Working Note and Wiki page with 
> named subsets of OWL that are provably polynomial based on Bernardo's current 
> document.

Could you explain what is the difference to the OWL Light from the 1.0
standard? You claimed yourself that that was broken. What is it that
makes the new approach different?

It is clear that different people have different ideas of what "broken"
means here. To me, the old OWL Light was computationally broken because
it wasn't really easier than full OWL DL. The same applies to the 
fragment that appeared on Zhe's slides, i.e., it seems ExpTime-hard.

> 1 - OWL Lite
> I propose we redefine OWL Lite to be closer to the current language coverage 
> that is in Oracle's OWL Prime.
> For the DL version of this, we will have a model theory and the restrictions 
> needed to prove whatever it is we wish to prove about it (completeness, 
> decidability, etc)
> There will be a Full version which is defined as the subset of the OWL Full 
> Semantics (however we end up defining those) corresponding to the same 
> language constructs (note: this may well require removing some language 
> features that Oracle and others currently support from this named subset)

I vote against this. I have sympathy for having *an* (not *the*) OWL
fragment that is motivated by database applications. But I absolutely
disagree with your approach of making this particular fragment, which
is not even remotely understood, the main OWL Light, and all the other
fragments just other fragments that are mentioned in some docs. From
my perspective (which may be different from yours), this would simply
mean repeating the mistake that was made with the original OWL Light
(which was a failure).

> 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.

> those DL restrictions required to keep this true - ie only inversefunctional 
> datatypes used as keys per Uli's presentation, or whatever).  This version 
> could be called something like RDFS 3.0 DB (if we get it close to datalog) or 
> DL (if that's the best we can do)

So there will be different versions of RDFS 3.0. I would like to raise
the question whether the OWL workgroup is the right place to do this.
Both in spirit and from the name, RDFS 3.0 seems to be much closer
to RDFS than to OWL. So shouldn't it be standardized in an RDF group?

> The language would likely be widely used (or more correctly, is already 
> widely used) -

I again point out that there are fragments that *are* widely used
already, which seems much stronger than "likely be widely used". These
fragments you want to send to a WG note. Again: I have sympathy for
what you are trying to do. But let me follow Jeremy and emphasize a
letter from our acronym OWL (though a different one): O is for
*O*ntology languages. I point out once more that very important
ontologies such as SNOMED, NCI, Gene ontology, and the medical
ontology produced by Sebastian for Siemens Health are written in
EL++. All of these ontologies are large-scale, professionally
supported, and used in real (even commercial) applications. Can you
say this of your (or any other) fragment? I cannot see that you do
justice to this when moving "all other fragments" to a WG note.


*      Carsten Lutz, Institut f"ur Theoretische Informatik, TU Dresden       *
*     Office phone:++49 351 46339171   mailto:lutz@tcs.inf.tu-dresden.de     *
Received on Saturday, 8 December 2007 10:00:12 UTC

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