- From: Jim Hendler <hendler@cs.umd.edu>
- Date: Tue, 22 Jan 2002 22:04:07 -0500
- To: las@olin.edu, Frank van Harmelen <Frank.van.Harmelen@cs.vu.nl>
- Cc: www-webont-wg@w3.org
At 4:23 PM -0500 1/22/02, Lynn Andrea Stein wrote: >I believe that we will have a difficult if not impossible time in >producing a "reasonable" default mechanism. > > ************ WARNING WARNING - CHAIR NEUTRALITY VIOLATION ****************** I am violating Chair neutrality for the sake of this message!! ************ WARNING WARNING - CHAIR NEUTRALITY VIOLATION ****************** The overwhelming "anti-default" span of this discussion forces me to mention that the "other half" of the KR world (the frames folks) have never had any real problem with defaults (or non-monotonicity). In fact, the semantic net systems we all derive our heritage from (DL or frame!) started with an argument that the nets allowed better encoding because one COULD have defaults, for example, it is a useful encoding to say MAMMAL --- birth-method ----> live AARDVARK --- ISA ---> mammal AARDWOLF --- ISA ---> mammal (500 mammal examples deleted) ZEBRA -- ISA ---> mammal and thus save ourselves 500+ assertions that these things are each live bearing. The exception PLATYPUS --- ISA ---> mammal PLATYPUS --- Birth-method ---> live causes no one any problems unless they are trying to use a classifier, which is why many of us frame folks don't like classifiers!! The key point I want to make is that it seems to me we are assuming that this sort of solution is bad a priori, because it is somehow "non-monotonic" -- yet there are effective inference procedures for this (polynomial if one excludes explicit "is not a" links) -- and, in fact, those system have scaled way beyond anything done in DLs to date (speed, size, assertion type, etc.) [1][2][3] I believe it is important that this group make considered decisions about how the extra utility of these constructs trades off with the logical cleanliness of the other. I would love to find a mechanism (for example the one Frank suggests seems to me to lead to something workable), or a "layering" (the way Dieter was using the term) which allows some coexistance of these things. Frame inference systems have been used in a lot more deployed systems than DL systems have and over a lot longer span of years, and it seems strange to me for us not to at least seriously explore the issues -- especially as Guus made very strong arguments for the need for this in all his use cases particularly cataloging and web site management, which are two of the areas in which actually deployed ontology systems are used regularly! -Jim H. [1] http://www.cs.umd.edu/projects/plus/Parka/aaai97.ps [2] http://www.cs.umd.edu/projects/plus/Parka/ppai.ps [3] A nice collection of papers on sem networks can be found in: Semantic Networks in Artificial Intelligence, edited by Fritz Lehmann, Pergamon Press, 1992. ************ WARNING WARNING - CHAIR NEUTRALITY VIOLATION ****************** I am violating Chair neutrality for the sake of this message!! ************ WARNING WARNING - CHAIR NEUTRALITY VIOLATION ****************** -- 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) AV Williams Building, Univ of Maryland College Park, MD 20742 http://www.cs.umd.edu/users/hendler
Received on Tuesday, 22 January 2002 22:07:56 UTC