Hi all I am trying to write a custom package builder in order to create rules programmatically. The most important feature are simple tests against object attributes like: "if (position.getValue() > 100) then" In Drools 3 I managed this the following way: LiteralDescr literalDescr = new LiteralDescr("value", ">", "100"); // define what class the rule refers to ColumnDescr columnDescr = new ColumnDescr("com.sample.bl.Position", "p"); columnDescr.addDescr(literalDescr); // assemble condition AndDescr andDescr = new AndDescr(); andDescr.addDescr(columnDescr); ruleDescriptor.setLhs(andDescr); packageDescriptor.addRule(ruleDescriptor); Upgrading to Drools 4 the above code breaks and in search of a replacement for ColumnDescr I stumbled across a FieldConstraintDescr which seems appropriate according to the Pattern Entity Relationship Diagram (Figure 6.11) of paragraph 6.5 in the documentation. Using it throws the following exception: Exception in thread "main" org.drools.RuntimeDroolsException: BUG: no builder found for descriptor class class org.drools.lang.descr.FieldConstraintDescr at org.drools.rule.builder.GroupElementBuilder.build(GroupElementBuilder.java:7 7) at org.drools.rule.builder.RuleBuilder.build(RuleBuilder.java:53) at org.drools.compiler.PackageBuilder.addRule(PackageBuilder.java:420) at org.drools.compiler.PackageBuilder.addPackage(PackageBuilder.java:283) What does that mean? Did I misunderstand the concept? Is there an easier way to achieve what I want? I appreciate any hints. Thanks and regards, Andreas