I think Jon Weygandt wrote:
> it looks like modifying a fact sometimes requires the equivalent of:
>
> For each slot modified
> {
> Retract the fact
> Set the slot
> Assert the fact
> }
Yes, more or less. Special versions of "retract" and "assert" can be
used to cut a few corners in this specific case, but that's just how
the Rete algorithm works. Same way re-hashing a hash table works, too,
if you think about it, more or less.
>
> Although in 6.1p7 it appears that from the rules modify accepts multiple
> slot/values and is optimized (whereas Rete offers only a single
> slot/value at a time) and 7.0b3 seems to do the inefficient loop.
>
Jess 6 and earlier would retract the fact, modify all the slots, then
assert. The current version of Jess 7 will do the whole cycle for each
modified slot. The reason for this is that the slot-specific
activation features need to know the slot that's been modified when
the assert is done. There are two ways to accomplish this: either
provide a collection of slot names and allow multiple simultaneous
modifies, or change things to really only modify one slot at a time,
and then pass around just the one slot name.
I've gone back and forth on which is better. Obviously it depends on
how frequently a program uses the multiple-modify syntax. If it's used
infrequently, then forcing the Rete network to iterate over all those
one-item collections is inefficient. If multiple-modify is used a lot,
then it's a net gain to pass the collections around.
My impression is that multiple modify -- i.e.,
(modify ?fact (slot-1 X) (slot-2 Y) (slot-3 Z))
is used infrequently. I'd be interested to hear otherwise, though!
---------------------------------------------------------
Ernest Friedman-Hill
Advanced Software Research Phone: (925) 294-2154
Sandia National Labs FAX: (925) 294-2234
PO Box 969, MS 9012 [EMAIL PROTECTED]
Livermore, CA 94550 http://herzberg.ca.sandia.gov
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