A General Practical Approach to Pattern Matching over Ziv-Lempel Compressed Text

We address in this paper the problem of string matching on Lempel-Ziv compressed text. The goal is to search a pattern in a text without uncompressing. This is a highly relevant issue, since it is essential to have compressed text databases where eecient searching is still possible. We develop a general technique for string matching when the text comes as a sequence of blocks. This abstracts the essential features of Lempel-Ziv compression. We then apply the scheme to each particular type of compression. We present the rst algorithm to nd all the matches of a pattern in a text compressed using LZ77. When we apply our scheme to LZ78, we obtain a much more eecient search algorithm, which is faster than uncompressing the text and then searching on it. Finally, we propose a new hybrid compression scheme which is between LZ77 and LZ78, being in practice as good to compress as LZ77 and as fast to search in as LZ78. We show also how to search some extended patterns on Lempel-Ziv compressed text, such as classes of characters and approximate string matching.