hes@ecsvax.UUCP (Henry Schaffer) (12/04/85)
DATA COMPRESSION by Gilbert Held
(Techniques and Applications
Hardware and Software Considerations)
John Wiley & Sons 1983 ISBN 0 471 26248 X $30.95
xii + 126 pages (94 text + appendices and index) 6"x 9"
This small book discusses the benefits of data compression for data
communications and data storage, discusses a number of data-compression
techniques (listed below) and discusses implementation and benefit
considerations. The orientation seems to be towards data communications
in an IBM oriented world, but ASCII data is also covered. (Even though
neither half duplex nor uuencode/uudecode are mentioned in the index, this
still could be a useful book for the un*x community.) In spite of what
the subtitle says, this is really a software book.
The core of the book is Chapter 2 which discusses the basis and
implementation of nine data-compression techniques:
Null Suppression (run length encoding for blanks/nulls)
Bit Mapping (use of a bit map to indicate locations of a commonly
repeated char)
Run Length Encoding
Half-Byte Packing (e.g., for EBCDIC or ASCI numeric digits
which vary only in the lower half-byte)
Diatomic Encoding (use of a special character to replace a pair of
characters)
Pattern Substitution (higher than di-atomic encoding - essentially
tokenization)
Relative Encoding (similar to delta modulation encoding, e.g., sending
the differences between successive values in a stream of
readings. This can be quite effective if the values
change slowly)
Forms Mode Operation (sending only the variable info from a screen)
Statistical Encoding (variable length char codes, with frequently used
ones being shorter - includes Huffman coding)
This book is easy to read, and should serve well as an introduction to data
compression techniques and benefits, and as a reference to the techniques
it covers. It is practically (vs. theoretically) oriented.
--henry schaffer