1. A method for generating, from a primary hierarchy of items, a plurality of custom browse hierarchies for unique subsets of the items in the primary hierarchy, the method comprising: generating each of the plurality of custom browse hierarchies, wherein the primary hierarchy comprises leaf nodes and one or more ancestor nodes of one or more of the leaf nodes, each leaf node defines a set of one or more items that meets at least constraints of each ancestor node of the leaf node, and the constraints of each ancestor node of the leaf node comprise one or more attribute names and one or more attribute values and wherein generating each of the plurality of hierarchies comprises: establishing a set of rules for at least the ancestor nodes of the primary hierarchy, wherein each rule in the set of rules is associated with one of the leaf nodes and each ancestor node of the leaf node and each rule comprises a logical aggregation of constraints specified by at least each ancestor node of the leaf node; and performing by a computer system: identifying a subset of the set of rules, wherein each rule in the subset has constraints that are met by at least one of the items in the unique subset of items; for each leaf node in the primary hierarchy, including the leaf node in the custom browse hierarchy if the rule associated with the leaf node is included in the subset of the set of rules; for each ancestor node in the primary hierarchy, including the ancestor node in the custom browse hierarchy if at least one leaf node of the ancestor node is included in the custom browse hierarchy; and representing the custom browse hierarchy by all the included leaf nodes and included ancestor nodes of the primary hierarchy and the custom browse hierarchy represents a pared version of the primary hierarchy.