Patent ID: 7487143

Claim:
A method of categorizing information items using a hierarchical structure of nodes, wherein each information item is represented by a leaf node and each category is represented by a non-leaf node in said hierarchical structure, comprising: associating a first number with each node, wherein for each non-leaf node said first number is uniquely selected from a subset of relatively prime elements within a unique factorization domain, wherein said subset of relatively prime elements includes at least one non-prime element, wherein elements of said subset of relatively prime elements taken pairwise are all relatively prime to each other, and wherein for each leaf node said first number is equal to one; associating a second number with each node, wherein for each root node said second number is equal to said first number, and wherein for each non-root node said second number is equal to a product of said second numbers associated with each parent node of said non-root node and said first number of said non-root node; and relocating a given node together with its descendents from at least one old parent node to at least one new parent node by dividing out the second number of each old parent node, and by multiplying in the second number of each new parent node, with regard to the second number of the given node and the second numbers of all nodes that are descendents of the given node.