Hi Elena, Sorry I missed you on IRC earlier. Before addressing rule engine performance, you want to make sure you have a clear understanding of how the Rete algorithm works. This is the algorithm that drives most rule-based expert systems, including Drools. There's a great presentation series which explains Drools and Rete at a high level: http://salaboy.com/2011/03/17/drools-5-community-training-module-1-drools... http://planet.jboss.org/post/drools_5_community_training_module_4_rete_al... With that in mind, performance can vary greatly depending on the types of rules and the complexity and interrelationship between facts. The size of the data set itself (referred to as facts) is only one piece of the equation. If you have the money to spend, I'd highly recommend the "Performance" chapter of the Packt book available here: http://www.packtpub.com/drools-jboss-rules-50-developers-guide/book There's also a good discussion of the pros and cons of using a rule engine available here on stack overflow: http://stackoverflow.com/questions/2167358/pros-and-cons-of-java-rules-en... If you have more specific questions beyond the basics, as Wolfgang says, that's what this list is for. -- Build Smarter Software. Spantree Technology Group, LLC 813 W Randolph St, Suite 301, Chicago, IL email: cedric(a)spantree.net (mailto:cedric@spantree.net) | phone: 773.359.3865 (tel:773.359.3865) On Sunday, July 1, 2012 at 12:00 PM, elena_nardini(a)libero.it wrote: