Hi Folks,
I'm looking to use JESS in an alarm processor subsystem. I look to your
experience to let me
know if JESS is the right tools or if there is a better solution.
My main question is about handling temporal issues within JESS. Such as
rule timeouts. What i think I'm looking for is a
implementation of a watchdog timer or similar. Or maybe I've missed
something (like backward chaining : not sure I
understand that really ) that already accomplishes the following:
For example. Rule X fires is rules A, B and C fire. Rule X outputs the
message " A and B and C fired"
however Rule Y fires if rules A and C fire but rule B does not.
Rule Y outputs the message " A and C fired. But B failed to fire"
Now in my application the data can be received out of order and
sometimes due to faults are never received.
I would like rule Y to fire to signal that data has not been received
BUT only after an appropriate time out, in case the data is delayed
At the moment :
(A) fact asserted (i.e. data enters to satisfy rule A)
Rule A fires
(C) fact asserted
Rule C fires
Rule Y fires
"A and C fired. But B failed to fire"
(B) fact asserted
Rule B fires
Rule X fires
"A and B and C fired"
Net result : the operator sees a problem message where none exists.
Since this is output from the JESS engine,
the output cannot be recalled or de asserted like facts in working memory.
ideal solution :
Rule Y modified to fire only if (B) is not received 30 seconds after all
other conditions are met
(A) fact asserted
Rule A fires
(C) fact asserted
Rule C fires
Rule Y fires - but now waits till its timeout expires
< 16 seconds pass >
(B) fact asserted
Rule B fires
Rule Y expires as conditions are not met
Rule X fires
"A and B and C fired"
<reset>
(A) fact asserted
Rule A fires
(C) fact asserted
Rule C fires
Rule Y fires - but now waits till its timeout expires
< 31 seconds pass >
Rule Y fires as conditions are now met
"A and C fired. But B failed to fire"
PS. I would be willing to write this up for the wiki later if a good
JESS solution is hammered out.
Thanks
Gary
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