21. The system according to claim 20 , wherein the tuning unit tunes the structure by at least one of: deleting a category in which the number of assigned search results is less than a first threshold; and generating more detailed sub-categories for a category in which the number of assigned search results is larger than a second threshold.
20. The system according to claim according to claim 19 , further comprising: a matched structure tuning unit that tunes the matched structure, wherein the matched structure tuning unit comprises: a counting unit that counts a number of the assigned search results in each of the categories of the structure of the matching website; and a tuning unit that tunes the structure according to a result of the counting unit.