1. A method for mining at least one association rule based upon data in a database containing attributes, comprising: defining each of the attributes with a respective attribute values as an item, and defining the database as a plurality sets of items, and defining each of the sets of items in the database as a record; defining an item appearing in one of the sets as an affirmative item in the set, and defining an item absent from the set as a negative item in the set; and mining the association rule by applying at least one logical AND operation on an assumption of one association rule containing at least one negative item and at least one affirmative item so as to obtain a conclusion of the association rule containing at least one affirmative item.