Data compression system and apparatus

In a data terminal device which outputs a plurality of digital messages each including a plurality of redundant and non-redundant data characters in which a character is considered redundant if the character is the same in succeeding data messages, a data compression apparatus for compressing each of said digital messages comprising:

• means for serially outputting each character of the digital message;
• means for generating a first control signal in response to the outputting of each character of the digital message;
• counter means operated in response to the generation of each of said first control signals to output a predetermined count;
• timing control means coupled to said counter means for outputting a plurality of second control signals in response to the outputting of each count of the counter means;
• first storage means for storing a compressed data record;
• table lookup means storing a plurality of first non-redundant characters together with an associated one of a plurality of start of compressed data record characters coupled to said outputting means, said timing control means and said first storage means for receiving a first non-redundant character from said outputting means when enabled by one of said second control signals, said table lookup means outputting one of a plurality of a start-of-record characters to said first storage means in accordance with the first non-redundant character received, said start-of-record characters indicating the start of the compressed data record in addition to the first non-redundant character received;
• second storage means operated by one of said second control signals for storing a second non-redundant character of a digital message;
• third storage means operated by one of said second control signals and coupled to said outputting means for storing a second non-redundant character of each succeeding digital message received from said outputting means;
• compare means coupled to said second and third storage means for comparing the second non-redundant characters stored in said second and third storage means;
• and first bistable means coupled to said compare means and operable in response to the finding of no comparison by said compare means for enabling said first and second storage means to store the second non-redundant character outputted from said outputting means.

In a system for transmitting a plurality of data messages between a data terminal device and a central processor, said data messages including a plurality of characters representing redundant data in which a character is considered redundant if the character is the same in succeeding data messages and non-redundant data such as transaction data, merchandise-coded data and an operator ID data, an apparatus for compressing said data message comprising in combination:

• means for serially outputting each data character of the data message;
• means for generating a first control signal upon the outputting of each data character;
• means for generating an identifying signal upon detecting the start of the first character in the data message;
• binary counter means responsive to the generation of said identifying signal and said first control signal for generating a predetermined binary count;
• means for generating a plurality of clock pulses;
• timing control means operated in response to the generation of each of said binary counts and said clock pulses for outputting a plurality of second control signals, said timing control means include sequencing means for disabling said timing control means from generating said second control signals in response to the outputting of certain of said redundant data characters by said outputting means;
• first storage means for storing a compression data message;
• and table lookup means coupled to said outputting means, said first storage means and said timing control means for receiving a merchandise-coded data character when enabled by one of said second control signals, said table lookup means includes second storage means for storing a plurality of start-of-record characters each representing a merchandise-coded character, said table lookup means outputting to said first storage means one of said start-of-record characters in accordance with the merchandise coded character received wherein the start-of-record character stored in said first storage means represents the start of the compressed data message and the merchandise coded character outputted by said outputting means.

A method for use in an on-line data processing system in which data messages are transmitted from a data terminal device to a central processor of compressing redundant and non-redundant characters of a data message generated in a data terminal device upon the disabling of the central processor in which a character is considered redundant if the character is the same in succeeding data messages and said data terminal includes a storage table in which is stored a plurality of first non-redundant characters and an associated one of a plurality of different start-of-record characters comprising the steps of:

• sensing the disabling of the central processor;
• interrupting the data message transmitted from the terminal device upon sensing the disabling of the central processor;
• storing all redundant and non-redundant characters of the first interrupted data message;
• comparing all redundant characters of each data message with the redundant characters of a previous data message;
• eliminating all redundant characters of the data message upon finding a match with the corresponding character of a previous data message;
• comparing a first non-redundant character of the data message with the stored plurality of first non-redundant characters in said storage table;
• generating one of a plurality of different start-of-record characters in accordance with the matching of said first non-redundant character;
• storing in a first storage unit the start-of-record character generated as the first character of the compressed data record, the start-of-record character also representing the matched first non-redundant character;
• storing in a second storage unit a second non-redundant character of the first data message received which varies with a corresponding second non-redundant character in each succeeding data message by a constant value in said first storage unit as a character in said compressed data record;
• and disabling said second storage unit from receiving any subsequently received second non-redundant characters.