Re: daml:SymmetricProperty?

From: Jim Hendler (
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.

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!)

Dr. James Hendler
Chief Scientist, DARPA/ISO	703-696-2238 (phone)
3701 N. Fairfax Dr.		703-696-2201 (Fax)
Arlington, VA 22203

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