5. A document data processing method for document retrieval according to claim 4, wherein by mapping the character codes to a number of entry codes which is smaller than the number of the characters actually used, said bit list is realized by a number of bits which is smaller than a number of the character types actually used.
6. A document data processing method for document retrieval according to claim 5, wherein in association with said component character table search, a bit list in which one-bit information allocated to all usable characters is prepared for each of said documents and wherein bit positions for the characters used in the documents are set to "1s" respectively, while the bit positions for the characters not used in the documents are set to "0s", respectively; said component character table search is executed by searching said bit list having all the bit positions set to "1s" for all the characters constituting said search term.