Exact data compression using hierarchical dictionaries

Summary form only given, substantially as follows. This paper describes a new data compression/expansion algorithm which uses multiple (two as an example) dictionaries for storing previously encountered strings of the data file. The first dictionary is a short one, has 128 entries and needs 7 bits to store its address. The second dictionary is a long one, has 32768 entries and requires 15 bits to store its address. Each is initialized with frequently occurring strings. An input data file is compared with the dictionaries so that the longest substring which can be found will give its position in the dictionary as an output code. Compression and expansion use the same procedure to form and update dictionaries