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Re: Case for Reinstatement of Qualified Cardinality Restrictions

From: Ian Horrocks <horrocks@cs.man.ac.uk>
Date: Wed, 23 Apr 2003 15:40:31 +0100
Message-ID: <16038.42463.213081.933001@merlin.horrocks.net>
To: Jeff Heflin <heflin@cse.lehigh.edu>
Cc: Jim Hendler <hendler@cs.umd.edu>, Jonathan Borden <jonathan@openhealth.org>, webont <www-webont-wg@w3.org>

On April 22, Jeff Heflin writes:
> 
> I have serious concerns about reopening this issue. The chief reason it
> was omitted is that hardly any DAML users understood it and few (if any)
> attempted to use it. I'd like to see compelling evidence that things
> would be different if we added the feature back to OWL. I do not find
> Rector's comments compelling because
> 
> 1) It would be more compelling if the need for a particular DL feature
> came from somebody who wasn't in the DL community. It's not suprising he
> finds it important b/c he's been using it in his DL work. I find that
> some of Deborah's comments present a counter-point Rector's. She said
> the medical community that uses Protege has never requested this sort of
> feature. Furthermore, although she is experienced with DLs, believes
> QCR's can be confusing to novices.

Well, users of Protege are presumably also happy to have no negation,
no disjunction, no transitivity, no inverses and no way to distinguish
between universal and existential quantification
(some/allValuesFrom). On the other hand, it seems that many of them
believe meta-classes to be essential.

The bottom line is that you get used to whatever you are driving.

As far as novices are concerned, they can stick to Lite, or just avoid
using this feature!


> 2) Guus went through the use cases and found that only a and b were
> compelling use cases for reintroducing the feature. However, I think
> just because someone can come up with a use case for a semantic feature,
> does not mean we should add it. We chose to provide a language with
> restricted expressivity, otherwise we would have ended up with FOL or
> something more. I could come up with a very compelling use case for
> adding Horn logic rules (e.g., to say that the member of an organization
> is also a member of any super-organizations of the organization), yet
> that's no reason for us to open an issue on whether or not to add rules
> to the language.

It isn't a case of adding it so much as not taking it away - it was
there in DAML+OIL, and doesn't add any significant complexity to OWL
DL - in fact the systems that come closest to supporting OWL DL (i.e.,
FaCT and Racer) already have it. It seems that at least some users of
DAML+OIL have found this feature very useful and are unhappy to
discover that it disappeared from OWL.


> 3) I think the factor that makes QCRs most confusing in OWL is the
> difficulty in expressing them cleanly in triples. 

I prefer not to comment on triple based syntax!

Regards, Ian
Received on Wednesday, 23 April 2003 09:40:20 GMT

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