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Re: Issue: Add hasValue to OWL Lite

From: Jim Hendler <hendler@cs.umd.edu>
Date: Thu, 12 Dec 2002 09:12:17 -0500
Message-Id: <p05111709ba1e481e9cad@[10.0.1.2]>
To: Ian Horrocks <horrocks@cs.man.ac.uk>
Cc: Frank van Harmelen <Frank.van.Harmelen@cs.vu.nl>, www-webont-wg@w3.org

A
>
>
>3. For ExpTime logics, it is possible to devise relatively simple
>algorithms that are goal directed and know when they are done. It has
>also been demonstrated that these algorithms can be optimised so as to
>give good performance in realistic applications.
>
>4. For NExpTime logics, no such algorithm is known. This is
>illustrative of just how significant the jump from ExpTime to NExpTime
>is from both a theoretical and a practical perspective.

but OWL DL is in the NExpTime class - right?  And there are 
implementations for that - so it's not like adding hasValue makes OWL 
Lite unimplementable.  My argument is simple - the hasValue is easily 
dealt with compared to some other features of OWL DL (particularly 
conjunctions and disjunctions of unnamed class constructs).  I think 
OWL Lite is already harder than I would like it to be, but this 
feature is not worse than not having it to those of us who want to 
use this langauge subset (which, as I understand it, doesn't include 
you).

   More importantly, I know of no work around for not having hasValue. 
For some other things (classes as instances for example) there are 
well known ways to kludge it, so people oculd stay in LITE without 
using those features.  For hasValue, we're talking basic definitional 
properties.  The only workaround I know of is inverseFunctional on 
datatypes (I.e. one uses strings as keys), but that is much worse 
because that workaround takes us into FULL.

>
>
>>  In short, you are arguing that adding hasValue makes the worst case
>>  computational complexity of OWL Lite to be the same as that of OWL
>>  DL.  OK, I'm willing to admit that.  However, the working group never
>>  agreed that we were limiting Owl lite based on worst case complexity
>>  -- in fact, you yourself argued that the only argument in favor of
>>  Lite is ease of implementation -- okay, I throw that back to you --
>>  Jos and I have argued this is not hard to implement.  In my case, it
>>  is naturally implemented by databases, which are often optimized for
>>  these sorts of tasks.
>
>As I mentioned in my earlier email, this depends on your definition of
>"implement", and on just what it is you want to implement. To me, a
>prerequisite for implementation is having an algorithm.

right, and if there is no algorithm AT ALL then OWL DL wouldn't work. 
Since there are algorithms, we're back to what you argued for in the 
first place, implementational ease - but that is not equivalent to 
computational complexity, which seems to be our point of difference.

Again, I think we have reached as far as we can in arguing, and it is 
time to vote.

>
>Also, as far as OWL Lite -v- OWL DL is concerned, if what you are
>saying about "implementation" is true, then OWL DL is equally easy to
>implement and there is no requirement whatsoever for OWL Lite. If it
>makes you feel better, you could "re-badge" OWL DL as OWL Lite.

Ian, that's facile and you know it, and as I said before, we're not 
willing to reopen that issue
  -JH

-- 
Professor James Hendler				  hendler@cs.umd.edu
Director, Semantic Web and Agent Technologies	  301-405-2696
Maryland Information and Network Dynamics Lab.	  301-405-6707 (Fax)
Univ of Maryland, College Park, MD 20742	  240-731-3822 (Cell)
http://www.cs.umd.edu/users/hendler
Received on Thursday, 12 December 2002 09:12:31 GMT

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