| 摘要 |
A system of the present invention stores: a first index which designates lists of keywords contained in texts from identifications of the respective texts; a second index which designates lists of texts containing keywords from identifications of the respective keywords; and the number of texts containing the respective keywords. Then, upon receiving an input of a text search condition, the system calculates an estimation of search time by the first index and an estimation of search time by the second index, and determines which one of the first and second indexes makes a search faster. Then, by using the index which has been determined to make the search faster, the system searches for keywords which appear in texts satisfying the text search condition with higher frequency.
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