I think James Owen wrote: > ... But, back to the original supposition (Same > data, same rules, same engine) if you don't get the same result then you > have a real problem.
Only if "time" is part of the data. In a multithreaded environment (a.k.a. a real-world environment) this isn't true. As long as data is arriving asynchronously from rule execution, the ordering of arrival of facts can change the outcome. Only if a rule engine is running in a single, self-contained thread can this be considered to be true. Otherwise, any rule like "if X and not Y" will fire differently depending on the order in which X and Y arrive, because if X gets there first, then at one point, X is true, but not Y. This is how the real world works. Remember the TV commercials in which the hapless diner eats something nasty and then whacks herself on the forehead in realization and exclaims, "I could have had a V8!" If the V8 cart had arrived before the hot-dog cart, the outcome would have been different; but in the real world, either outcome is equally likely. There's also the old puzzle about the man with two girlfriends who live at opposite ends of town, and he takes the first train that arrives randomly to visit either girlfriend. But he sees one 9 times more often than the other. Why? Because the trains run ten minutes apart, one on the nines, the other on the tens. He's only got a one-minute window in which he'll get on the tens train. In a static production-system world, he'd visit both equally often. In the real world, not so much. Now, this single, self-contained thread model is actually very common in the rule-engine biz; most commercial rule engines assume that you'll stuff in some objects, run the engine, and then extract the results. You can use Jess this way, but you can also have the data arrive continuously and asynchronously while processing continues. This isn't the classical model of a production system anymore, but it's a much more useful model in real software. --------------------------------------------------------- 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? Notify [EMAIL PROTECTED] --------------------------------------------------------------------
