A system for information item categorization in which each non-leaf node in a hierarchical organization of nodes represents a category, and each leaf node represents an information item. A number P is associated with each node. For non-leaf nodes, the associated number P is selected from a subset of relatively prime elements chosen from an appropriate Unique Factorization Domain (UFD), such as a set of relatively prime numbers which are a subset of the familiar set of integers. For leaf nodes, P is set to 1. A number M is also associated with each node. For each root node, M is set to the value of P for that node. For each non-root node, M is set to the product of the M's of all parent nodes of the node and the P of that node.