Abstract: A decision operation tree (“DO Tree”) according to the present invention is a logical tree representation of decision making rules and actions instituted according to those rules. In preferred embodiments of the invention, one or more DO Trees are tailored to serve a user's rating and billing system needs. According to the present invention, Do Trees are comprised of a plurality of nodes and branches, which branches connect the nodes together in a descending relationship. Any node may have defined for it one or more actions (whose implementation can be prioritized or ordered) which are triggered whenever the node is reached. Those nodes having branches stemming (“descending”) from them have two parameters, a Decision Attribute and a Branching Type, which defines the node's relationship with its descending branches. Upon occurrence of the predefined event, the method includes proceeds from node to node, and optionally performs one or more actions in each node.