| 摘要 |
PROBLEM TO BE SOLVED: To speedily search a leading search key among search keys having a search object key value regardless of the number of search keys having the same key value included in a search object key column. SOLUTION: When a search instruction including a search object key value is inputted by a user, a search key having the search object key value is searched by a binary search method from an array type index A by a key search part SK. Afterwards, one of a linear search method or the binary search method is selected based on a threshold to be determined according to the rate of a duplicate level calculated by a duplicate level determination part D to the mean costs of the linear search method and the binary search method by a boundary search part 11. At that time, when the duplicate level is less than a threshold, the linear search method is selected, and when the duplicate level is the threshold or more, the binary search method is selected. Afterwards, the leading search key of the search keys having search object key values is searched by the selected search method. COPYRIGHT: (C)2007,JPO&INPIT
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