Document Listing for Queries with Excluded Pattern

Abstract

Let $\mathcal D$ = {d ₁,d ₂,...,d _D } be a given collection of D string documents of total length n. We consider the problem of indexing $\mathcal D$ such that, whenever two patterns P ⁺ and P − comes as an online query, we can list all those documents containing P ⁺  but not P −. Let t represent the number of such documents. An index proposed by Fischer et al. (LATIN, 2012) can answer this query in $O(|P^+|+|P^-|+t+\sqrt{n})$ time. However, its space requirement is O(n ^3/2) bits. We propose the first linear-space index for this problem with a worst case query time of $O(|P^+|+|P^-|+\sqrt{n}\log \log n+\sqrt{nt}\log^{2.5} n)$.

This work is supported in part by Taiwan NSC Grant 99-2221-E-007-123 (W. Hon) and US NSF Grant CCF–1017623 (R. Shah).