Brian, let me take a stab at answering your questions. On Feb 11, 2008 5:46 PM, Brian Trezise <Brian.Trezise(a)intellidata.net&gt; wrote: That's because Drools's LHS do not allow function calls. "containsKey()" is a function call. Drools cannot guarantee how often left-hand sides are evaluated, so to rule out side-effects, function calls are forbidden altogether. Providing an operator to test for containment in a map's keys is another improvement request I submitted, please add a comment to http://jira.jboss.org/jira/browse/JBRULES-1457 if you need that too. If your map does not contain NULL values, you can use the MVEL operator [] like so: pFamilies[SchemaConstants.CERAMIC_CHIP_CAPACITORS] != null I'm not aware of local variables (though they would certainly be useful, maybe similar to Scheme's let) - To avoid clobbering the code with literals like that, I usually put them into Java code, e.g. Utils.Patterns.MarkedPattern = "MAR(K|KE|KED)?"; Newlines should not be significant. - Godmar