DATA COMPRESSING APPARATUS AND A DATA DECOMPRESSING APPARATUS, A DATA COMPRESSING METHOD AND A DATA DECOMPRESSING METHOD,AND A DATA COMPRESSING OR DECOMPRESSING DICTIONARY CREATING APPARATUS AND A COMPUTER READABLE RECORDING MEDIUM STORING A DATA COMPRESSING PROG

A data compressing technique and a data decompressing technique provide a compressing dictionary storing unit for storing a compressing dictionary usable when data to be compressed is compressed, a compressing dictionary use or non-use deciding unit for deciding whether the compressing dictionary is to be used or not when the data to be compressed is compressed, and a coding unit for coding the data to be compressed on the basis of the compressing dictionary when the compressing dictionary use or non-use deciding unit decides the compressing dictionary is to be used, whereas not coding but outputting the data to be compressed when the compressing dictionary use or non-use deciding unit decides the compressing dictionary is not to be used, thereby stably achieving a preferable compression ratio for a small quantity of data such as text data in a text file.