This system is provided with a keyword conversion table for converting and rewriting synonyms, etc., in a document to be registered into a common registration keyword at the time of performing document registration, and a retrieving part converts a retrieval character string into a common registration keyword and then performs retrieval of a plurality of document data. 文献登録にあたり登録する文献中の類義語等を共通登録キーワードに変換して書き換えるためのキーワード変換表を備え、検索部は検索文字列を共通登録キーワードに変換してから複数の文献データを対象に検索を行う。 - 特許庁