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Re: Proposed response to Alan Rector (QCRs)

From: Jim Hendler <hendler@cs.umd.edu>
Date: Mon, 16 Jun 2003 12:41:04 -0400
Message-Id: <p05200f55bb13a1b7eec3@[]>
To: webont <www-webont-wg@w3.org>

Dan and I have discussed this via irc, here is yet another attempt to 
get it right:

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 

  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

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	  *** 240-277-3388 (Cell)
http://www.cs.umd.edu/users/hendler      *** NOTE CHANGED CELL NUMBER ***
Received on Monday, 16 June 2003 12:41:08 UTC

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