[rules-users] facts hierarchy

Hi all, i have a question concerning facts hierarchy, i'm looking for some hint as i suppose the same problem could have been faced by someone on the list. I try to eplain with an example: - Suppose to have a tree of facts, each object representing an UI widget. <root> <A id="1"> <B /> </A> <A id="2"> <B /> </A> </root> - The individual elements A(1), B, A(2), B are mapped to facts, that are inserted in a KnowledgeStatefulSession - A rule exists that states that when an object A is selected, the B object is automatically selected - An event occurs that causes selection of node A(1) The expected result is, obviously, that only the B element that is descendant of A(1) must be automatically selected I'm trying a way to express the 'descendant' relationship in LHS construct. The rule will look like: rule "A requires B" when $fact1: NodeFact(id == "A", selected == true) $fact2: NodeFact(id == "B", selected == false, this DESCENDANT-OF $fact1) then $fact2.setSelected(true); end What is, in your opinion, the best way to handle this situation? What should replace the fake "DESCENDANT-OF" match? Do i need to use a function that returns the list of descendant nodes of $fact1 and then match $fact2 against that? Will this be fast when dealing with large trees? Any suggestion will be appreciated, thank you. Giovanni