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Method for Incorporating Data Conversion into Text Compression Scheme

IP.com Disclosure Number: IPCOM000106011D
Original Publication Date: 1993-Sep-01
Included in the Prior Art Database: 2005-Mar-20
Document File: 2 page(s) / 81K

Publishing Venue

IBM

Related People

Greer, TD: AUTHOR [+4]

Abstract

Disclosed is a method for incorporating data conversion into a text compression scheme. The anticipated application is in transferring text files between computers using ASCII coded text and computers using EBCDIC coded text. In such a situation, a conversion between the two formats must be made if the file is to continue to be human-readable on the new system. The workstation LAN File Services/VM product does this, for example, so that files stored on the host are accessible to both PC (ASCII) and VM (EBCDIC) users.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Method for Incorporating Data Conversion into Text Compression Scheme

      Disclosed is a method for incorporating data conversion into a
text compression scheme.  The anticipated application is in
transferring text files between computers using ASCII coded text and
computers using EBCDIC coded text.  In such a situation, a conversion
between the two formats must be made if the file is to continue to be
human-readable on the new system.  The workstation LAN File
Services/VM product does this, for example, so that files stored on
the host are accessible to both PC (ASCII) and VM (EBCDIC) users.

      Another feature of some systems which store and retrieve data
(like Workstation LAN File Services/VM) is data compression.  Some
lossless compression algorithm is used to reduce the amount of space
a file takes up, either after it is transferred from PC to host (in
order to reduce the storage space required) or before (in order to
reduce the file transfer time, and possibly also to reduce storage
space).  Before the file can be used, it must be decompressed.  These
two functions of ASCII/EBCDIC conversion and
compression/decompression traditionally have been done separately.
In this disclosure, we show how to combine these two functions and
thereby eliminate the processing time associated with the
ASCII/EBCDIC conversion.

      In [*]  "Dynamic Dictionary" methods of employing standard LZ
compression algorithms is discussed.  In a Dynamic Dictionary
compression scheme, the compression program begins with a dictionary
of (typically) all the possible text characters, and adds to the
dictionary as it compresses the file.  When decompressing a file, the
decompression program starts with the same beginning dictionary and
uses the same algorithm as the compression program to add to its
dictionary.  The dictionaries are thus built up dynamically, and
hence the name.

      But suppose the beginning compression dictionary and the
beginning decompression dictionary do not match.  The decompression
dictionary will be built up as before, so that the output file will
be the same as the input file, except that the characters will be
altered according to th...