2. The apparatus of claim 1 , wherein different hierarchy levels are separated by placing a symbol between hierarchy assigned values, and the search results are determined from a limited initial search space comprising the documents stored from previous searches.
2. The apparatus of claim 1 , wherein different hierarchy levels are separated by placing a symbol between hierarchy assigned values, and the search results are determined from a limited initial search space comprising the documents stored from previous searches. 3. The apparatus of claim 2 , wherein the clustering module determines a number of steps between a sequence of hierarchy locations based on a number of symbols between the sequence of hierarchy locations.