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Re: Proposed response to Alan Rector (QCRs)

From: Dan Connolly <connolly@w3.org>
Date: 16 Jun 2003 12:00:06 -0500
To: Jim Hendler <hendler@cs.umd.edu>
Cc: webont <www-webont-wg@w3.org>
Message-Id: <1055782806.27168.176.camel@dirk.dm93.org>

On Mon, 2003-06-16 at 11:41, Jim Hendler wrote:
> Dan and I have discussed this via irc, here is yet another attempt to 
> get it right:

Yes, this seems responsive to the comment and consistent with WG

Please send it.

> Dear Alan:
>    Let me start by thanking you for your comments -- this commented 
> generated much discussion in the working group, all available in the 
> public archives of www-webont-wg.  I will try to summarize the 
> discussion and results here, you are, of course, welcome to explore 
> the public archives - some pointers will be provided to make this 
> easier.
>   Briefly, DAML+OIL had a relatively ad hoc mechanism for representing 
> Qualified Cardinalities.  The WG observed that this was a rarely 
> used, and hard to describe, feature (not necessarily the notion of 
> QCRs, but the odd language features needed to implement them).  We 
> thus had decided to remove this feature.
> Based on your Last Call comment, we reopened and reconsidered this 
> issue.  As you can see from [1], it became clear to the group that we 
> needed a better mechanism than what was in DAML+OIL to handle this 
> issue (and also to handle some other aspects of qualification, for 
> example see [2] which discusses the need to also qualify functional 
> restrictions).  A better mechanism than the one in DAML+OIL for 
> representing QCRs was suggested [3], but unfortunately it became 
> clear to the group that this would be a major change to the language. 
> We therefore decided to reopen the issue of Qualified Cardinality 
> Restrictions, and then to POSTPONE this issue with a pointer to Guus' 
> proposal.  The specific decision to postpone is recorded in [4], the 
> rationale accepted by the group, and recorded in ourissues document 
> [5] is summarized as:
>   	 The Working Group decided 25 Apr 2002 to remove qualified 
> cardinality constraints. The issue was reopened due to new 
> information Apr 2003 from Alan Rector. In the 8 May 2003 
> teleconference, the WG resolved     ... to POSTPONE this issue for 
> the following reasons:
>   * OWL already contains one QCR construct: owl:someValuesFrom (QCR 
> with minimal cardinality of 1) which covers some frequent-occurring 
> cases of QCRs.
>   * There are some workarounds for QCRs, using the rdfs:subPropertyOf 
> construct. These can be used in simple cases, such as the example in 
> the Guide below. The WG agrees that these workarounds are more 
> problematic for complex part-of relations such as pointed out by Alan 
> Rector in his use cases a) and b).
>   * The evidence on whether users need this is mixed. Rector's use 
> cases are compelling, but Protege (which has a large user community) 
> has not reported user requests for this feature.
>   * Inclusion of this feature will put additional burden on 
> implementations. For example, it is nontrivial to add this to 
> Protege.     The Working Group therefore POSTPONES the full treatment 
> of QCRs, while considering possibilities for making idioms or other 
> guidelines for QCRs available to the community.
>   We hope that eventual follow on activities to our working group,, 
> will include a general mechanism for handling qualification. 
> However, adding these to OWL at this time would be a major step, and 
> would require significant effort as, in some cases, there is no 
> obvious implementation of these properties that can work with the 
> current OWL design.
> Please let us know if this decision to (a) acknowledge that our 
> design is lacking, but (b) postpone further design work to a future 
> version is acceptable.
>    -Jim Hendler
> [1] http://lists.w3.org/Archives/Public/www-webont-wg/2003Apr/0176.html
> [2]
> http://lists.w3.org/Archives/Public/www-webont-wg/2003May/0074.html
> [3]
> http://lists.w3.org/Archives/Public/www-webont-wg/2003May/0072.html
> [4]
> http://lists.w3.org/Archives/Public/www-webont-wg/2003May/0120.html
> [5]
> http://www.w3.org/2001/sw/WebOnt/webont-issues.html#I3.2-Qualified-Restrictions
> [6]
> http://www.w3.org/TR/webont-req/
Dan Connolly, W3C http://www.w3.org/People/Connolly/
Received on Monday, 16 June 2003 12:59:44 UTC

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