1. A method of processing a stabbing query comprising: obtaining a signal representative of said stabbing query; identifying nodes in a tree, said tree being stored in a memory, each of a plurality of sets being associated with one or more nodes of said tree, which are candidate nodes for being associated with at least one set which is stabbed by said stabbing query, each of said sets being associated with a score; for at least one of said candidate nodes, determining whether at least one unselected one of said sets associated with said candidate node is stabbed by said stabbing query and, if said at least one of said unselected sets associated said candidate node is stabbed by said stabbing query, determining a highest scoring unselected set associated with said candidate node which is stabbed by said stabbing query; selecting an unselected set from among highest scoring sets associated with candidate nodes which are associated with at least one unselected set which is stabbed by said stabbing query, wherein a node is eliminated as being a candidate node if said node is not associated with an unselected set that is stabbed by said stabbing query; and repeating said determining and said selecting until a specified number of sets are selected.