- From: Jim Hendler <hendler@cs.umd.edu>
- Date: Mon, 16 Jun 2003 12:41:04 -0400
- 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 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/ -- 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