9. The method of claim 8 , wherein: a rule in the set of rules comprises an antecedent and an inference, the inference being determined if the antecedent is determined as true; an inference is a numerical value or a set of rules; and the rule engine recursively evaluates rules in the primary set of rules to determine inferences until an inference that is a numerical value indicating an applicable discount type is found.
8. The method of claim 7 , wherein: the set of rules comprises a primary set of rules and a secondary set of rules; said primary set of rules is used to determine applicability of the discount type; and said secondary set of rules is used to determine a discount value for the discount type, the secondary set of rules being called for processing if the discount type is determined to be applicable.