The aggregation method includes computation method and judgment method. Procedure of computation method is as following: (1) through hash function, attribute of value is mapped into 32-bit vector, i.e. one piece of binary integer; (2) calculating TAG - ID =V1 & V2 &...& Vn , where & denotes 'bit oriented AND' calculation; (3) calculating V1 | V2 |...| Vn , where | denotes 'bit oriented OR' calculation. Procedure of judgment method is as following: it is to determine whether a vector is in set (V1, V2, ... Vn) from TAG - ID / MASK. Magnitude of amount of redundant information is related to misjudge ratio. But, if number k of different bit in mapped bit vector is as small as possible, enough localities are reached so as to make misjudge ratio smaller. |