1. A method using item constraints to discover association rules contained in a database, the method comprising: finding large itemsets in a database that satisfy defined constraints, the defined constraints involving one or more items of a mining input expression; determining subsets of large itemsets included in the itemsets, an itemset being large if its support is greater than a minimum support value, where support value for an itemset is based upon the number of times the itemset appears in the database; and finding association rules from the large itemsets that satisfy the defined constraints.