Longest Fragment First Algorithms for Data Compression

On-line text-compression algorithms are considered, where compression is done by substituting substrings of the text according to some fixed dictionary (code book). Due to the long running time of optimal com- pression algorithms, several on-line heuristics have been introduced in the literature. In this paper we analyse two modified version of an old algo- rithm introduced by Shuegraf and Heaps [8]. We will investigate the worst case behaviour of this Longest Fragment First (LFF) algorithm for several types of special dictionaries