what about implementing the approach Paul Haley used in ART for backward chaining?
http://haleyai.com/wordpress/2008/03/11/goals-and-backward-chaining-using-the-rete-algorithm/ paul recently posted his old paper on his blog. peter On Tue, Aug 26, 2008 at 12:40 PM, Ernest Friedman-Hill <[EMAIL PROTECTED]> wrote: > On Aug 26, 2008, at 11:55 AM, Marcin Krol wrote: >> >> I have to say that daisy-chained backward-chaining rules are decidedly >> non-trivial (and therefore harder to write and debug), while >> forward-chaining rules are very easy to understand (at least for me). >> >> I'm writing about Jess in my thesis on AI techniques, and so I wanted to >> ask you a few questions - is backward-chaining is really valuable in >> practice, outside of subjects like calling queries to databases (like in >> the example you give in "Jess in Action")? >> >> If so, where do you think it is most useful? Are there any problems that >> are awkward to code using forward-chaining while they are more natural >> to code using backward-chaining rules? > > > I think the most important applications have been the query-like ones. There > are certainly > plenty of techniques that work well with classical backward-chaining rules, > but really can't be > implemented using Jess's restricted form of backward chaining > . >> >> How do you think backward-chaining adds to the expressive power of Jess >> understood as language? Is it worth the effort, both for rule engine >> developer and for the rule engine user? > > I think it *could* add tremendously to the expressiveness of the language if > it were carried > further. There are a lot of problems that can be expressed elegantly with > backtracking, for example. > There have been some user-modified versions of Jess that implement > backtracking concepts, but none of them > in an elegant way, AFAIK. Right now I think the truth is that beyond the > query-like applications (which are > equivalent in many ways to "finders" in JRules), Jess's backward chaining > hasn't seen widespread use. > >> >> >> I have sort of stumbled on one limitation of backward-chaining in Jess: >> constraints on slots, I found I couldn't call a function on slot: >> >> Jess> Jess reported an error in routine ReteCompiler.addRule. >> Message: Can't use funcalls in backchained patterns __data. >> >> Is there a way around that? Or am I misunderstanding the problem, >> because one perhaps doesn't want to constrain slots in backward-chained >> rules as finding their values is the goal of this part of rule engine >> operation (as constraints would simply prevent firing one of b-c rules >> in the chain of reasoning in some cases, like it happened in my >> uncorrected example)? > > > There's no way around it in the current version of Jess. As you know, goals > are represented > as regular facts, and stored in regular working memory. For anything other > than literal constraints to > be usable in goals, there would need to be a way of representing the > constraint in the fact itself, and > storing that representation in working memory. While not impossible to > implement, this would impact many parts > of the Jess codebase. > > Another approach would be to store goals not in working memory, but in a > different > structure altogether, one designed from the beginning to accommodate their > requirements. > In retrospect this is probably how Jess's backward chaining should have been > implemented > in the first place. > > > --------------------------------------------------------- > Ernest Friedman-Hill > Informatics & Decision Sciences, Sandia National Laboratories > PO Box 969, MS 9012, Livermore, CA 94550 > http://www.jessrules.com > > > > > > > > -------------------------------------------------------------------- > 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] > -------------------------------------------------------------------- > > -------------------------------------------------------------------- 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] --------------------------------------------------------------------
