1. An apparatus for categorizing a plurality of objects which together comprise an object set, wherein a respective categorization value is associated with each object in said set, said apparatus comprising: a request handler for modifying said categorization value of one of said objects or for one of deleting one of said objects or adding a further object to said object set; data storage means for storing a global rating value which is calculated based on each categorization value of all of said objects in said object set; compound means for recalculating said global rating value responsive to invocation of said request handler; and modifying means for modifying said global rating value by employing an aggregation algorithm, wherein said aggregation algorithm recursively includes each one of said plurality of objects; and wherein said modifying means includes means for identifying and tracking each object for which said categorization value is included in said global rating value such that said aggregation algorithm includes said categorization value of each object of said plurality of objects a predetermined number of times.