1. A method of generating a plurality of custom browse hierarchies each representative of a unique subset of items, said method comprising: for each leaf node of a primary hierarchy representative of the items: establishing a search rule that comprises an aggregation of constraints specified by the leaf node and its ancestors; and executing code in a data processing system in accordance with the search rule to identify all of the unique subsets that contain at least one of the items meeting the aggregation of constraints; and executing code in a data processing system to create a custom browse hierarchy for each of the unique subsets, said creating further comprising retaining in the custom browse hierarchy only those leaf nodes, and their ancestors, from the primary hierarchy for which the unique subset has been identified by said identifying.