A system and method are provided for managing a knowledge base system storing a plurality of data instances, each data instance including at least one field, each field having at least one item and provided with an associated field type indicating whether the field is allowed to have only a single item or multiple items. At least one large itemset is determined by generating a plurality of itemsets formed of possible combinations of items selected from items corresponding to fields of the stored data instances. Itemsets having a combination of more than one item corresponding to a field having an associated field type indicating that the field is allowed to have only a single value are eliminated. The remaining itemsets are processed for generating associate rules.