PURPOSE:To prevent lowering of a retrieving speed by providing a bit table consisting of bit string for designating all data numbers of a data section in multiplex system for each predetermined character, and thereby reducing number of steps for retrieving. CONSTITUTION:When data are inputted, data number is designated to the data and stored in the coordinate of a data section together with the data number. Then, characters included in the data are extracted, and block address of a primary bit table and addresses corresponding to each character of secondary bit table are made to logic 1. When character string is inputted at the time of information retrieving, the content of addresses corresponding to each character in the primary bit table is logical product operated between the same bit positions, and the contents of addresses corresponding to each character are logical product operated between the same bit positions for each of the secondary bit table according to the result. Basing on the result, data of corresponding data number are read out from the data section.
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