I have a question regarding creating a list of items that are all in nested collections of my main object. A high level overview of the model is like this: public Level0 { private List<Level1> level1List; } public Level1 { private List<Level2> level1List; } public Level2 { private Date occurence; } Now, I add objects of type 0 in the working memory and for each of those objects, I want to find the latest occurrence of a certain Level2, regardless of which level1 they belong to. If there's only 2 levels and I want to find the latest occurrence of Level2's with a certain name, I can write: rule "latest level 1" when $l0: Level0() $date: Date() from accumulate (Level1(name in ("name1", "name2"), $occurence: occurence) from $l0.level1List, maxDate($occurence)) then // register fact that latest occurrence of name1/name2 level1 was on $date end Now, with 3 levels, since I obviously can't replace $l0.level1List with $l0.level1List.level2List, is there a way to create an intermediate list that will contain all Level2 objects? No filtering needs to take place on Level1, but if there's a way to do that too, that would be nice. What I currently have is this: rule "latest level 2" when $l0: Level0() $l1: Level1() from $l1.level1List $l2List: List(size > 0) from collect( Level2(name in (("name1", "name2")) from $l1.level2List ) $date: PartialDate() from accumulate (Level2( $occurence: occurence) from $l2List, maxDate($occurence)) then // register fact that latest occurrence of name1/name2 level2 was on $date end But this does not work as it treats each Level1 seperately: it creates a "latest occurrence" for all accumulated level2 facts within a level1, instead of one for the entire set of level 2's 'owned' by the level0 object. Any suggestions?