Abstract: A character string of which a start point is each address of character string data in an input buffer is rearranged in the predetermined order, so that a rank list is generated. Next, the location of the matching candidate of a character string to be encoded is obtained on the basis of the rank list. Then, the character string to be encoded is compared with a matching candidate, thereby obtaining a matching length. Further, a code is generated using the location of the matching candidate and the matching length, and the code is output as compression data.

Abstract: Provided is a probabilistic statistical data compression/restoration method for variable-length encoding a source character and restoring a variable-length code to a character using the probability of occurrence of the source character which appears following a character string (context) of n characters which immediately precede the source character. When variable-length encoding is performed, a context registration unit successively registers context based upon an entered character without fixing the length (degree) of context, and a compressing encoder selects registered context satisfying a predetermined condition, e.g., registered context for which the frequency of occurrence is greater than a fixed value, as context (encoding context) used in encoding, and variable-length encodes a source character by using this encoding context. A restoration unit restores a code to a character by executing processing which is the reverse of the processing executed by the compressing encoder.

Abstract: A data compression apparatus is capable of compressing data at a high compression rate and at a high speed. A data decompression apparatus is used in combination with this data compression apparatus to decode the compressed data. The data compression apparatus includes a RAM which stores Huffman code trees each of which corresponds to a character string, i.e. "context." A CPU encodes each character which is to be encoded by use of a Huffman code tree corresponding to the context at that time. Each time a character is encoded, the Huffman code tree used is reconstructed so as to account for the encoded character. The data decompression apparatus stores Huffman code trees corresponding to contexts respectively, decodes the code to be decoded by use of a Huffman code tree corresponding to the context (a character string previously decoded). Each time one character is decoded, the Huffman code tree used for decoding is reconstructed so as to account for the decoded character.

Abstract: A data compressing method involves the use of a data string registering unit for registering a charactor or charactor string and the context and a code information registering unit for registering coding information of the character or character string following the context, the coding information following previous a input data. The data compressing method includes a data string new registering step of, when the input character or character string and the context set is not registering in the string registering unit, register the set in the data string registering unit.

Abstract: In a data compressing apparatus, when a data input unit inputs unit data, a coding unit obtains an order corresponding to the input unit data and outputs a code corresponding to this order with reference to a compression table. When completing this coding process, a compression table updating unit changes the order of the unit data in the compression table in a self-organizing manner based on only that order. In a data restoring apparatus, when a code input unit inputs the code as a result of the compression, a data restoring unit obtains another corresponding to the inputted code and outputs the unit data corresponding to this order with reference to a restoration table. When completing this coding process, a restoration table updating unit changes the order of the unit data in the restoration table in the self-organizing manner based on only that order.