From: Libor Nenadál <libor.nenadal(a)gmail.com&gt; Subject: Re: [rules-users] Why is a flat object recommended? To: rules-users(a)lists.jboss.org Date: Thursday, August 13, 2009, 9:56 AM Mark Proctor wrote: > > We can exploit cartesian products and indexing for == constraints. If > its a nested model we have to iterate over all possible instances. The > other problem is if the nested model changes the engine has no idea this > has happened, which if you are not careful can lead to data integrity > issues. > I think that plain flat model is too limited for real life. In fact in most situations you just cannot avoid nesting. For example when I try to search for cars with 4 cylinder engine the best approach I found is: rule "get 4 cylinder cars"   when     Car ( $e: engine != null ) // car without engine? where are we? :)     Engine ( cylinderCount == 4 ) from $e   then     System.out.println("Found 4 cylinder car."); end This should be quite effective. I doubt that the following solution with cartesian product has the same complexity: rule "get 4 cylinder cars"   when     $e: Engine ( cylinderCount == 4 )     Car ( engine == $e )   then     System.out.println("Found 4 cylinder car."); end Using approach Car ( engine.cylinderCount == 4 ) tends to raise NullPointerException and I had problems with assigning the cylinderCount to variable so this was not a way to go for me. But this is not much a problem for me as I am a programmer and I can understand the rule language and data structures. But when business users are to edit rules (using Guvnor as the tool of choice) we come to troubles. I think that guided editor for rules does not allow "from". More importantly - can you create such a structure for a test scenario? I failed. :( -- View this message in context: http://www.nabble.com/Why-is-a-flat--object-recommended--tp15567690p24954... Sent from the drools - user mailing list archive at Nabble.com. _______________________________________________ rules-users mailing list rules-users(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users