| 摘要 |
PROBLEM TO BE SOLVED: To select a retrieving method with highest retrieval efficiency out of plural retrieving methods corresponding to retrieval conditions by providing a specified retrieving method selecting means. SOLUTION: A retrieving method selecting means 1 selects one retrieving method out of plural retrieving methods corresponding to the retrieval conditions including a retrieval pattern, namely, the number of keywords as character strings. In this case, when the length of the shortest keyword is short, an AC method is adopted, for example, and when the length of the shortest keyword is comparatively long and there is only one keyword, a BM method or a Sunday method is selected, for example. Further, when the length of the shortest keyword is comparatively long and there are plural keywords, the value of discrimination function depending on the number and length of these keywords is found and the AC method or a FAST method is used corresponding to that value. Thus, the retrieving method considered optimum is automatically selected corresponding to the retrieval conditions such as the number of keywords and the length of the shortest keyword.
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