10. The system of claim 9 and assigning newly received documents further comprising: placing a newly received document in a sub-cluster within a selected cluster.
10. The system of claim 9 and assigning newly received documents further comprising: placing a newly received document in a sub-cluster within a selected cluster. 11. The system of claim 10 wherein placing the received document in the sub-cluster based on matches between a sub-cluster vector indicating word occurrence in documents in the sub-cluster and a document vector indicating word occurrence in the newly received document.