19. A document data processing method for retrieving a document containing at least a search term designated by an operator from a document database registering therein document information in terms of character code data while referring to textual content of said document, comprising steps of: upon registration of text documents in said document database, creating condensed texts by decomposing each of textual character strings of the documents to be registered into fragmental character strings on the basis of at least one of character species including katakana character, hiragana character, kanji character, alphabetic character, numeric character and symbol character and checking mutual inclusion relations possibly existing among said fragmental character strings resulting from said decomposition, to thereby create a plurality of condensed texts separately on a character species basis, each of said condensed texts being constituted by the fragmental character strings of a same character species while excluding any character string found to be included by other character string; creating a component character table describing the species of the characters occurring in registered texts; registering in said document database said plurality of character-species based condensed texts together with said component character table in addition to the text of the document to be registered; and upon retrieval of the document containing the designated search term, executing first a component character table search for thereby extracting those documents which contain all the species of characters constituting the search term designated by the operator by consulting said component character table; executing subsequently a condensed text search by consulting the condensed text corresponding to the character species of the fragmental character strings constituting the search term designated by the operator in the documents extracted through said component character table search for extracting only the documents corresponding to the condensed texts which contain the fragmental character strings constituting the search term designated by the operator to thereby select the documents containing the designated search term; and executing finally a text body search for extracting a document which satisfies query condition imposed on the search term by consulting the texts of the documents extracted through said component character table search and said condensed text search.
19. A document data processing method for retrieving a document containing at least a search term designated by an operator from a document database registering therein document information in terms of character code data while referring to textual content of said document, comprising steps of: upon registration of text documents in said document database, creating condensed texts by decomposing each of textual character strings of the documents to be registered into fragmental character strings on the basis of at least one of character species including katakana character, hiragana character, kanji character, alphabetic character, numeric character and symbol character and checking mutual inclusion relations possibly existing among said fragmental character strings resulting from said decomposition, to thereby create a plurality of condensed texts separately on a character species basis, each of said condensed texts being constituted by the fragmental character strings of a same character species while excluding any character string found to be included by other character string; creating a component character table describing the species of the characters occurring in registered texts; registering in said document database said plurality of character-species based condensed texts together with said component character table in addition to the text of the document to be registered; and upon retrieval of the document containing the designated search term, executing first a component character table search for thereby extracting those documents which contain all the species of characters constituting the search term designated by the operator by consulting said component character table; executing subsequently a condensed text search by consulting the condensed text corresponding to the character species of the fragmental character strings constituting the search term designated by the operator in the documents extracted through said component character table search for extracting only the documents corresponding to the condensed texts which contain the fragmental character strings constituting the search term designated by the operator to thereby select the documents containing the designated search term; and executing finally a text body search for extracting a document which satisfies query condition imposed on the search term by consulting the texts of the documents extracted through said component character table search and said condensed text search. 20. A document data processing method for document retrieval according to claim 19, wherein said text body search is executed when said search term is constituted with a plurality of character species and when said query condition includes a positional condition of the search term in the next text.