Hi, So essentially the solution is to use either a name slot or an id slot and use it to store in other facts.
This was a dummy test example. I am using a more complicated rule set wherein i dont have numeric ids or names for all the facts. Hence the only option is to use the fact-id's for joining. thanks, --- [EMAIL PROTECTED] wrote: > > This was an interesting one. OK, here's the deal. > > 1) You create a bunch of facts. In particular, > there's a "class" fact > whose "course-id" slot contains a reference to a > "course" fact whose > "title" slot is "History". This is an actual Java > reference to the > "course" jess.Fact object. > > 2) You clone all the facts, and store the clones in > an array > list. Here's where things start to go wrong: the > cloned "class" fact's > course-id slot still contains a reference to the > *non-cloned* course fact. > > 3) You reset the engine and assert the cloned facts. > Now there's a > slot in a class fact containing a reference to a > course fact that > isn't in working memory. > > 4) When Jess does the pattern matching for > > > (defrule change-professor > (class (course-id ?course1)) > ?course1 <- (course (title "History")) > > Jess binds the ?course1 variable to the slot > contents, which is a > reference to the old fact. Then it checks if the > "course" fact in > working memory is "equal" to this one. In this > context, the equality > check is just a comparison to see that the numeric > fact-id's are the > same -- under normal circumstances, this suffices. > Jess actually can't > use an identity test (for reasons that I won't go > into now) so this is > unlikely to change. Anyway, this test passes, even > though the two > variables refer to different fact objects, because > they have the same > ID, and normally two facts in working memory can't > have the same ID, > so these look like the same fact. > > 5) Then when the RHS of this rule tries to modify > ?course1, you get an > exception because, essentially, you're passing a > Fact to (modify) > which is not in working memory. > > So, what should you do? Well, if "course" had an > "ID" slot that held a > numeric ID for a course, then you could put that > into the course-id > slot of class and your general scheme would then > work fine. Just do > the joining using the id slot rather than the > fact-id of the course. > > > > > I think =?iso-8859-1?q?Moderator?= wrote: > [Charset iso-8859-1 unsupported, filtering to > ASCII...] > > Hi, > > > > i want to store the facts from the rete engine, > fire > > the rule and load back the previous facts and fire > the > > rule again. > > heres a briefing of what i am doing > > > > 1. clone each fact and store it in the arraylist > > 2. fire the rule. > > 3. Assert the fact one by one from the arraylist > using > > rete.assertFact(fact) method. > > 4. fire the rule. > > > > The rule is very simple: it modifies a slot of one > of > > the facts. First time the rule fires properly > without > > any errors. How ever when the rule fires second > time > > following exception is thrown. > > > > Jess reported an error in routine Funcall.execute > > while executing (modify ?course1 (professor ABC)) > > while executing defrule MAIN::change-professor. > > Message: Error during execution. > > at jess.Funcall.execute(Funcall.java:273) > > at jess.Defrule.fire(Defrule.java:215) > > at jess.Activation.fire(Activation.java:84) > > at jess.Agenda.run(Agenda.java:203) > > at jess.Agenda.run(Agenda.java:183) > > at jess.Rete.run(Rete.java:1097) > > at Test.main(Test.java:32) > > Caused by: java.lang.NullPointerException > > at jess.FactList.assignTime(FactList.java:40) > > at jess.Rete.processToken(Rete.java:952) > > at jess.FactList.finishModify(FactList.java:347) > > at > jess.FactList.modifyRegularFact(FactList.java:382) > > at jess.FactList._modify(FactList.java:303) > > at jess.Rete._modify(Rete.java:433) > > at jess.Modify.call(Funcall.java:971) > > at > jess.FunctionHolder.call(FunctionHolder.java:30) > > at jess.Funcall.execute(Funcall.java:266) > > ... 6 more > > > > I am attaching the .clp file and also the .java > file > > herewith. > > I guess the problem is occuring as i am asserting > the > > facts with the rete.assertFact() method. Hence the > > rule is not able to modify the fact slots. > > > > How do i put the facts back in the rete engine? > > > > thanks in advance, > > > > sanket. > > > > > ________________________________________________________________________ > > Send free SMS using the Yahoo! Messenger. Go to > http://in.mobile.yahoo.com/new/pc/ > Content-Description: Test.java > > [Attachment, skipping...] > Content-Description: test.clp > > [Attachment, skipping...] > > > > --------------------------------------------------------- > Ernest Friedman-Hill > Distributed Systems 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 > > -------------------------------------------------------------------- > 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? 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