Overview of Cliffy's taxonomy indexing and compression approach. (A) Shows an example taxonomy in which d = 10 and an example tree order that guides the generation of the text of the taxonomy prior to building an index. (B) Visualizes the difference between the document array profiles and the cliff-compressed document array profiles. The cliff-compressed document array profiles consist of a “main table” with a fixed number of columns as well as an “overflow table” that stores any pairs that could not be included in the main table. (C) Using a profile (i.e., row of document array profiles) as an example, it visualizes cliff compression at the index building step, followed by how each profile is used at query time for either the lowest common ancestor query or approximate document listing.