A computer calculates, in accordance with a maximum mean discrepancy, a similarity level between a first feature distribution correlating to a first distribution information item stored in a distribution database and a second feature distribution correlating to a second distribution information item stored in the distribution database. The second distribution information item is different from the first distribution information item. The maximum mean discrepancy is a distance measure indicative of the similarity level between the first and second feature distributions. The computer determines whether the calculated similarity level is equal to or higher than a predetermined threshold, and integrates the first feature distribution and the second feature distribution into a common feature distribution upon determining that the calculated similarity level is equal to or higher than the predetermined threshold.