Regarding your comment for DAO's in the WHEN clause. I'd say that's a very strong anti-pattern. In general our approach has been to look for the absence of the fact being inserted, and move the DAO call into the THEN clause. I'm sure you're thinking, "what if my DAO doesn't return anything?" See the next discussion on breadcrumbing. Drools will fire your DAO call on every agenda scan (IE: whenever a fact is inserted, modified, or retracted) if it's included in the WHEN clause. The other two tools we've used are to create what we call a "bootstrap" agenda and use "breadcrumb" facts. The bootstrap agenda is made up of a small set of rules that handle loading up initial facts for our rule set. Using simple "Breadcrumb" facts you can cut down on rescans/execution of rules. We created a simple RuleBreadcrumb object that contains a "name" attribute. Note, we don't use breadcrumbing for all rules. We mostly use them in the bootstrap phase because there are a lot of unrelated changes going on in working memory and there's a risk that the DAO may not return a fact. Putting it all together it looks something like this: rule "Start Bootstrap Agenda" salience 100 when GoalsRequest(memberID != null) not RuleBreadcrumb(name == "Start Bootstrap Agenda") then drools.setFocus("bootstrap"); insert(new RuleBreadcrumb("Start Bootstrap Agenda")); end rule "Load Some Fact Bootstrap" agenda-group "bootstrap" when not RuleBreadcrumb(name == "Load Some Fact Bootstrap") SomeOtherCriteria(anAttribute != null) then insert(new RuleBreadcrumb("Load Some Fact Bootstrap")); insert(myDao.getSomeData()); end So while I wouldn't call this a "best practices" document, those are at least 2 patterns we've found to be performant and quite useful in our own rule development. Macon -----Original Message----- From: rules-users-bounces(a)lists.jboss.org [mailto:rules-users-bounces@lists.jboss.org] On Behalf Of Brice Figureau Sent: Tuesday, February 09, 2010 4:40 AM To: Rules Users List Subject: [rules-users] Rules writing best practice? Hi, Is there a rules writing best practice document somewhere? I'm asking the question because as a newbie rule writer (which doesn't know anything about the underlying drools matching algorithm), I'm wondering if my rules will behave gracefully. For instance, I (ab)use a lot the from/accumulate to bring in the knowledge some external facts coming from some DAO. All my rules use one time or more the same "from dao.getInformationFromDatabase( <inserted fact> )" structure and I'm not sure the algorithm is smart enough to cache this information which is constant for a given inserted fact. Should I instead insert all this information as facts prior to the rules firing? -- Brice Figureau My Blog: http://www.masterzen.fr/ _______________________________________________ rules-users mailing list rules-users(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users