A search index structure which extends a typical composite index by incorporating an index which is optimized for fast retrieval from storage and which eliminates data which is specific to phrase searching. Other data is represented in a manner which allows it to be calculated rather than stored. Associating variable length entries with logical categories allows their length to be inferred from the category rather than stored. Using delta values between document IDs rather than the ID itself generates a compact, dense symbol set which is efficiently compressed by Huffman encoding or a similar compression method. Using an upper threshold to remove large, and thus rare, delta values from the symbol set prior to encoding further improves the encoding performance.