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Re: Proposed response to Martin Merry, HP

From: Jim Hendler <hendler@cs.umd.edu>
Date: Wed, 14 May 2003 08:11:07 -0400
Message-Id: <p05200f28bae7d54e8781@[]>
To: Jeremy Carroll <jjc@hpl.hp.com>, www-webont-wg@w3.org

(note - there is a suggestion to editors for some wording changes to 
Ref and Guide in this message - it is before the section marked 
personal opinion)

At 8:44 AM +0300 5/14/03, Jeremy Carroll wrote:
>>  On closer examination of the comment, it seems
>>  to be more about what goes in OWL DL than
>>  what goes in OWL Lite.
>And in ...
>>Please help me find the relevant decisions
>>and/or find evidence that those implementations
>>pass some relevant tests and/or add an
>>issue to the issues list.
>In January, we agreed a definition of a "complete OWL DL consistency checker",
>if we had evidence that such a thing existed, and/or that more than one would
>exist in the future (and the WG was satisfied that they would be practically
>usable, rather than essentially theoretical exercises) then we could respond
>with a message that indicated that, and that we thought that that was
>sufficient to justify the DL level.
>If we don't have such evidence then I agree with
>>  Mr. Merry's point, "We're concerned that OWL users should have their
>>  expectations met when they use OWL compliant systems." seems well
>>  made, no?

So let's set their expectations correctly -- we did try, by the way - 
in Reference, section 8.2 we say:

In particular, the OWL DL restrictions allow the maximal subset of 
OWL Full against which current research can assure that a decidable 
reasoning procedure can exist for an OWL reasoner.

and in 8.3 we say

The limitations on OWL Lite place it in a lower complexity class than 
OWL DL. This can have a positive impact on the efficiency of complete 
reasoners for OWL Lite.

In fact, my original response to Mr. Merry was going to be that we 
had already addressed his comments and point out these quotes --- 
However, his comments and a couple of others we received show that we 
haven't made the difference clear ENOUGH in our documents.  (For 
example, in section 1.2 we don't mention the computational issue).  I 
therefore suggest that editing Ref and Guide to set expectations is 
the correct solution - consistent w/WG decisions in the past.

One we could fix ref, is to make it clear that the difference between 
OWL Lite and OWL DL with respect to this computational issue is 
there.  For example, when we first introduce Lite in section 1.2 of 
ref we say:

OWL Lite is particularly targeted at tool builders, who want to 
support OWL, but want to start with a relatively simple basic set of 
language features.

instead of saying it is known to have a relatively efficient decision 
procedure (and citing the literature).  Maybe simply adding a 
sentence after the one I cite above that says

"In addition, OWL Lite is designed based to fit into a known 
computational class that, while exponential, is lower than the 
complexity of OWL DL [cite something]"

I also think the "Species of OWL" section of the Guide is also less 
clear than it could be, and might be wordsmithed to make the issue 
clearer (for example, OWL Lite could say "Desirable computational 
properties" and OWL DL could say "maximal decidable subset, although 
subject to a higher worst-case complexity")

Guus, Mike S -- would making these edits be acceptable?   If so, I 
would include in the response to Merry and to the other similar 


>(A danger is that if OWL DL is tainted then the whole OWL brand is tainted).

What I would say would make OWL DL "tainted" would be to remove oneOf 
and hasValue.  hasValue is used in about 10% of the ontologies in the 
DAML ontology library, and oneOf, although not heavily used in that 
library, is IMHO necessary for mapping existing sources into 
ontologies --my group has used it in many cases where we have used 
either an XML schema or a database schema as the basis of an 
ontology, especially in our work with Web Service Composition [1].  I 
would also remind the group that we actually had support in the WG to 
put hasValue in Lite, but decided not to due to the computational 

I would argue strongly that it is better to explain things more 
clearly in our documents than to change the language.  We spent a 
long time developing a language that is well balanced for many 
considerations, and I'd like to see if used in practice before we 
start cutting useful features because of computational issues that 
may rarely or never arise in real applications. For instance, 
PARKA-DB [2], still the fastest ontology management system deployed 
to date, is in the same complexity class as OWL DL, but somehow 
people don't seem to mind since it can answer most useful queries in 
a few milliseconds against ontologies with tens of thousands of 
classes - it has a worst case time that could be in several minutes 
for the largest ontologies built yet - but that doesn't seem to 
matter since after 5 seconds it asks the user if they want to 
continue, and most people say "no" and reformulate the query...

Quoting one of our comment raisers, speaking about OWL:

At 11:43 PM -0400 5/9/03, Bijan Parsia wrote in [3]:
4) Get the damn thing out the door.


[1] http://www.mindswap.org/papers/composition.pdf
[2] http://www.cs.umd.edu/projects/plus/Parka/aaai97.ps

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)
Received on Wednesday, 14 May 2003 08:11:15 UTC

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