I'm trying to write a custom navigation portlet, using the core NavigationPortlet as a model to access the appropriate JBP apis, but keeping track of when I need a node vs. when I need the corresponding PortalObject instance is driving me nuts. The PortalObject model (pages,portals,windows) makes sense, but I can't follow what additional structure the nodes provide. Can someone provide a quick description of the intended purpose of each hiearchy, and when I need to go between each?

Thanks,
Peter