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Re: defaults

From: Frank van Harmelen <Frank.van.Harmelen@cs.vu.nl>
Date: Tue, 22 Jan 2002 17:46:27 +0100
Message-ID: <3C4D9763.4E34988D@cs.vu.nl>
To: www-webont-wg@w3.org
"Smith, Michael K" wrote:
> 
> 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.

And Tim Finin wrote:

> I think the only answer to providing some support for defaults is to do it
> they way it's been done in KL-TWO (as I recall) and Classic.  The idea was,
> if I remember right, to include conventions for providing defaults that
> was outside the core of the language and for which no semantics was given.
> This would give people with a strong need for working with defaults a
> standard way to do it in OWL without doing damage to the semantics of
> the core language.  Perhaps a few years of experimentation 
> with the mechanism would help us engineer a better solution.

I want to add my voice to the above. 

- On the one hand, we will not be able to come up with a treatment of defaults that is both commonly accepted, formally sound and computationally tractable (we seem to have wide agreement on this)

- On the other hand, there are many application areas where some form of defaults are absolutely required, and in fact provide some of the main justifications over purely text-based solutions. (We seem to have some, but perhaps not universal agreement on this)

Like Mike and Tim above, I think we should simply provide the syntactic hooks for "defaults" (whatever they may mean), so that implementors can do with it what they like. (This puts defaults in the same category as version-labelling, I would think). 

To be clear: I don't particularly like this approach (I don't think anybody does), but it is  simply a practical way out of a thorny issue. 

Frank.
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Received on Tuesday, 22 January 2002 11:46:30 GMT

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