Compressed Text Databases with Efficient Query Algorithms Based on the Compressed Suffix Array

Abstract

A compressed text database based on the compressed sufffix array is proposed. The compressed suffix array of Grossi and Vitter occupies only O(n) bits for a text of length n; however it also uses the text itself that occupies $O(n\log |\Sigma |)$ bits for the alphabet ∑. On the other hand, our data structure does not use the text itself, and supports important operations for text databases: inverse, search and decompress. Our algorithms can find occ occurrences of any substring P of the text in $O(|P|\log n + occ\log ^\varepsilon n)$ time and decompress a part of the text of length l in $O(l + \log ^e n)$ time for any given 1 ≥ ∈ > 0. Our data structure occupies only $n(\frac{2} {\varepsilon }(\frac{3} {2} + H_0 + 2logH_0 ) + 2 + \frac{{4log^\varepsilon n}} {{log^\varepsilon n - 1}}) + o(n) + O(|\Sigma |log|\Sigma |)$ bits where ${\rm H}0 \leqslant {\text{log}}\left| \sum \right|$ is the order-0 entropy of the text. We also show the relationship with the opportunistic data structure of Ferragina and Manzini.