The.Algorithm.Design.Manual.Springer-Verlag.1998

Text Compression
Next: Cryptography Up: Set and String Problems Previous: Approximate String Matching
Text Compression
Input description: A text string S.
Problem description: A shorter text string S' such that S can be correctly reconstructed from S'.
Discussion: Secondary storage devices fill up quickly on every computer system, even though their
capacity doubles each year. Decreasing storage prices have only increased interest in data compression,
since there is now more data to compress than ever before. Data compression is the algorithmic problem
of finding alternative, space-efficient encodings for a given data file. With the rise of computer networks,
a new mission for data compression has arisen, that of increasing the effective bandwidth of networks by
reducing the number of bits before transmission.
Data compression is a problem for which practical people like to invent ad hoc methods, designed for
their particular applications. Sometimes these outperform general methods, but often they do not. The
following issues arise in selecting the right data compression algorithm:
● Must we exactly reconstruct the input text after compression? - A primary issue in data
compression algorithms is the question of lossy versus lossless encodings. Text applications
typically demand lossless encodings, because users become disturbed whenever their data files
file:///E|/BOOK/BOOK5/NODE205.HTM (1 of 4) [19/1/2003 1:32:11]