Hi again, Thanks for the quick and clear answer on my question on combining backward chaining and CEs.
Now I got another problem: Suppose there are a number of account facts in Jess' working memory: (account (id 1) (value 2000)) (account (id 2) (value 8000)) (account (id 3) (value 4000)) ... Now I want a rule that fires for all accounts together, not for each one seperately: (defrule sum-of-all-account-values (logical (account (id ?a&) (value ?value1))) (logical (account (id ?b&:(> ?b ?a)) (value ?value2))) (logical (account (id ?b&:(> ?c ?b)) (value ?value2))) ... (logical (not (exists (account (id ~?a&~?b&...)) => (assert (sum (+ ?value1 ?value2 ...)))) The conditions (> ?b ?a), (> ?c ?b) were added to make sure the rule would only fire for the combination of all accounts once. Now, the problem isn't to get the correct sum. In a former version of my application I calculated it by getting all accounts with a defquery and then using the returned Iterator object to get the desired sum. My problem is to make the sum fact logically dependent of all account facts used to compute it. If an old account fact is modified or retracted, or a new one is asserted, I want the sum fact to be retracted automatically. I presume there isn't a good solution to this, as this is a typical problem for rulebased systems, but I could be wrong. Right now, I use a rule that first gets the number of accounts, by using the count-query-results function, and then uses this number to build a rule with the build function. The resulting rule has a salience of 100, so it gets executed right after is is build. It has the same number of (logical (account ...)) patterns as there are accounts, plus the (logical (not (exists (another-account)))) pattern. After it asserted the fact, it undefrules itself. This works, but is very errorprone and hard to read, not to mention the possible effects of other rules with salience 100 or auto-focus rules in other modules. Regards, Steffen. -------------------------------------------------------------------- To unsubscribe, send the words 'unsubscribe jess-users [EMAIL PROTECTED]' in the BODY of a message to [EMAIL PROTECTED], NOT to the list (use your own address!) List problems? Notify [EMAIL PROTECTED] --------------------------------------------------------------------
