21. The computer readable medium of claim 19 , wherein: the programming instructions comprise a rule engine implemented by rule programming, the rule engine comprising a set of rules and a processing relationship between a plurality of rules in the set of rules; and executing the downloaded programming instructions comprises applying the rule engine to product and order information associated with the purchase order to determine applicability of the discount type and to determine a discount value when the discount type is applicable to the order.
21. The computer readable medium of claim 19 , wherein: the programming instructions comprise a rule engine implemented by rule programming, the rule engine comprising a set of rules and a processing relationship between a plurality of rules in the set of rules; and executing the downloaded programming instructions comprises applying the rule engine to product and order information associated with the purchase order to determine applicability of the discount type and to determine a discount value when the discount type is applicable to the order. 22. The computer readable medium of claim 21 , wherein the rule engine comprises a recursive rule program, wherein resolution of a first rule requires resolution of a second rule, wherein the recursive rule program performs an automatic process that recursively calls itself.