From: Jim Hendler (jhendler@darpa.mil)
Date: 03/01/01
> Might also be worth > > considering whether there are other levels of this (transitive > > closure, for example) that we might want to consider - > > i.e. > > Driveable(X Y) is the transitive closure of Landborder(X Z) > >Transitive closure would also be a real extension to the expressive >power of the language. Although the extension wouldn't change the >complexity class of the language, there is good evidence to suggest >that empirical tractability would be seriously damaged by adding >transitive closure. > >Ian unless one happens to have developed the world's fastest transitive closure inferencing -- see the papers on PARKA-DB(TM; patent pending) :-> Seriously, we need to be careful that we don't throw out important functionality and expressivity that could be of use to tool designers, because of the logical issues -- in many cases people pre-compute a lot of the transitive relationships (like ISA) so they can get better performance -- even if the logic engine doesn't take this into account, it can be very important for performance of more "ad hoc" systems -- I worry often as to whether we are letting the logical purity of DAML+OIL get in the way of things programmers want - so far we've hit pretty good workable solutions -- I am now looking, however, for what the joint committee does after the current language moves into some sort of stabilization process (W3C or otherwise), and that's going to almost necessarily take us into something either more expressive, more "useable", more complex, etc. so my earlier message was just to get us thinking of the next level up, not meant to be something added to current langauge as is. (another layer of the layercake - what fun!) -JH Dr. James Hendler jhendler@darpa.mil Chief Scientist, DARPA/ISO 703-696-2238 (phone) 3701 N. Fairfax Dr. 703-696-2201 (Fax) Arlington, VA 22203 http://www.cs.umd.edu/~hendler
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