Compressing Inverted File Index Using Mixed Delta/Flat Binary Code

By clustering d-gaps of an inverted list strictly based on a threshold, and then encoding clustered and non-clustered d-gaps using different methods, we can tailor to the specific properties of different d-gaps and achieve better compression ratio. Based on this idea, in this paper we propose a cluster based mixed approach for inverted file index compression: mixed delta/flat binary code. Experiment results show that the new coding scheme achieves better performance in terms of compression ratio comparing to interpolative code which is considered as one of the most efficient bitwise codes at present. Besides, the new code has much lower complexity comparing to interpolative code and therefore enable faster encoding and decoding.