1. A system for determining a correlation between categories of a hierarchical taxonomy for documents, comprising: a taxonomy distance component that provides for each pair of categories in the taxonomy a taxonomy distance; a term space distance component that provides for each pair of categories in the taxonomy a term space distance indicating distance between term feature vectors representing terms of documents within the categories; and a metric component that provides a correlation metric indicating correlation between pairs of categories based on the taxonomy distance and term space distance between the categories of the pair.