So I simply fire a property change from setAdviceText? Do I need to
register Jess in some fashion as a listener?
Thanks.
On Dec 9, 2006, at 1:39 PM, Ernest Friedman-Hill wrote:
On Dec 9, 2006, at 2:53 PM, J Michael Dean wrote:
The GlucoseDecision.setAdviceText() is a trivial setter.
OK, that's all we need to know. The GlucoseDecision class supports
PropertyChangeListeners, and Jess takes that as a promise that
whenever setX() is called, an "X has changed" event will come back.
Until that event has come, Jess's working memory image of that
object is unchanged. Since your setter breaks the contract and
doesn't send the event, Jess loses track of the values of your
object's slots.
So here's the scenario. Imagine that the "adviceText" slot contains
something, we'll call it "?X". You call the equivalent of
(modify ?decision (str-cat ?X "more advice"))
Jess then calls setAdviceText(?X + "more advice"), and then that's
what the object contains. But working memory isn't updated until
the change event comes back -- and in this case, it never does. Now
working memory and the object are out of sync, and this is bad.
Then the next rule fires and it calls
(modify ?decision (str-cat ?X "even more advice"))
and so Jess calls setAdviceText(?X + "even more advice"). The value
of ?X is the same since working memory was never updated. The text
"more advice" is completely lost! That's what's happening here.
So there are two different ways to fix this. First, you can
explicitly tell Jess to ignore your PropertyChange mechanism, since
it's broken. To do this, you could say '(definstance
GlucoseDecision ?decision static)' instead of '(add ?decision)'.
For "static" definstances -- those that don't have
PropertyChangeListeners -- the 'modify' function changes both
working memory and the Java object.
The other way would be to fix setAdviceText so that it sends an
appropriate event after setting the property value.
---------------------------------------------------------
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://www.jessrules.com
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