Drools:
http://www.jboss.org/drools/documentation
http://docs.jboss.org/drools/release/6.0.1.Final/drools-docs/html/KIEChapter.html#KIEExamplesSection
http://docs.jboss.org/drools/release/6.0.1.Final/drools-docs/html/ch19.html
http://www.mastertheboss.com/drools/jboss-drools-tutorial
http://www.slideshare.net/hemapani/rules-programming-tutorial
http://www.infoq.com/articles/Rule-Engines