1. A method comprising: receiving a service usage request, wherein the service usage request represents, at least in part, a request for service usage received from a subscriber, the service usage request comprises a value pair, and the value pair comprises a first value, and a second value; identifying a zone item by traversing a configurable zone model tree, wherein the traversing is performed using the first value, and the second value; identifying a zone name of the zone by determining whether the service usage request occurred during a validity period for an entry in the zone item, wherein the validity period is defined by a start time and an end time specified by the zone item; and returning the zone name of the zone, wherein the zone item comprises the zone name, and the zone name identifies a charging structure to be used in satisfying the service usage request.