Faster Compressed Top-k Document Retrieval

Abstract

Let D = {d₁, d₂,...d_D} be a given collection of D string documents of total length n, our task is to index D, such that whenever a pattern P (of length p) and an integer k come as a query, those k documents in which P appears the most number of times can be listed efficiently. In this paper, we propose a compressed index taking 2|CSA| + D logn/D + O(D) + o(n) bits of space, which answers a query with O(t_sa log k log^ϵ n) per document report time. This improves the O(t_sa log k log^1+ϵ n) per document report time of the previously best-known index with (asymptotically) the same space requirements [Belazzougui and Navarro, SPIRE 2011]. Here, |CSA| represents the size (in bits) of the compressed suffix array (CSA) of the text obtained by concatenating all documents in V, and t_sa is the time for decoding a suffix array value using the CSA.