From: Jim Hendler ([email protected])
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 [email protected]
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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