RE: defaults

It seems clear that we cannot impose default reasoning on our description
logic framework.  

If defaults are really needed to support an 'input completion' model, there
is a potential, but ugly and partial, solution.  At the f2f we identified a
number of features we seem to be leaning towards that will not be given a
semantic interpretation by any formal definition.  This broad category of
annotations includes support for versioning (though this could be made part
of the namespace formalization), lexical labeling, and perhaps 'frame
description' information (designed to recapture details of the original
input grouping of statements).  All of these elements will have an
operational significance for various uses of OWL, but no semantic weight.

Defaults could be considered in the same fashion.  They only way they would
enter into the formal reasoning process would be if some input tool, perhaps
one that took advantage of a 'frame description', added them if the user did
not contradict them.  Of course, once added they would be permanent.
Changing them would have non-monotonic consequences.

The primary reason that I see for even considering such a feature would be
if we expect ontology developers to add their own ad hoc version of this.
Are we going to see lots of 

<daml:Class ref:ID="Bird">
 <daml:restriction>
    <daml:onProperty rdf:resource="#DefaultMember"/>
    <daml:hasClass ref:resource="#FlyingThings"/>
 <daml:restriction>
</daml:Class>

Which in turn would lead to grotesque and ultimately unsuccessful attempts
to warp the system to reason about such forms.

- Mike

Michael K. Smith
EDS Austin Innovation Lab
98 San Jacinto, Suite 500
Austin, TX 78701
Work: 512 404-6683

-----Original Message-----
From: Enrico Motta [mailto:e.motta@open.ac.uk]
Sent: Tuesday, January 22, 2002 7:38 AM
To: Peter F. Patel-Schneider; schreiber@swi.psy.uva.nl
Cc: www-webont-wg@w3.org
Subject: Re: defaults

...

I agree with Guus that defaults are a good thing to have, given that 
they are ubiquitous in applications, but of course only if some 
'clean' mechanism can be designed for OWL.

Enrico

At 6:44 am -0500 22/1/02, Peter F. Patel-Schneider wrote:
>From: Guus Schreiber <schreiber@swi.psy.uva.nl>
>Subject: defaults
>Date: Mon, 21 Jan 2002 17:06:24 +0100
>
>>  Peter,
>>
>>  During the f2f you mentioned that some limited representation of
>>  defaults could be possible in OWL. Could you elaborate on that? That
would
>>  be very helpful.
>>
>[...]
>>
>>  Thanks, Guus
>
>There is a very common idiom, which I like to call ``input completion'',
>that works as follows.  I'll use frame terminology to describe input
>completion for two reasons: 1/ the processing is much clearer in frame
>terminology, and 2/ I hope that not using RDF terminology will help prevent
>misunderstandings.
>
>... 
>A coherent story for input completion is much harder to make for RDF, as
>RDF does not have definitions of objects, nor does it have ordered inputs.
>A coherent story for input completion is also difficult to make for
>description logics, and thus would be hard to make for OWL.
>
>peter

Received on Tuesday, 22 January 2002 10:19:45 UTC