19. A computer readable medium storing a computer program which when executed places an online purchase order, the computer program for execution by a client device from which the purchase order originates, the computer program comprising: a set of instructions for downloading, at the client device, programming instructions for determining applicability of a discount type for the purchase order, the programming instructions being downloaded from a set of server computers connected to the client device through a network; a set of instructions for executing said downloaded programming instructions to determine the applicability of the discount type to the purchase order such that for multiple changes to the purchase order said programming instructions are executed at the client device multiple times to determine the applicability of the discount type without requiring new programming instructions to be downloaded through the network, said determining automatically done without human intervention and without downloading further instructions from the set of server computers; a set of instructions for receiving changes to the purchase order; a set of instructions for executing said downloaded programming instructions to determine the applicability of the discount type to the changed purchase order without downloading new programming instructions through the network; and a set of instructions for placing the online purchase order to the set of server computers through the network in accordance with the applicability of the discount type determined at the client device.
19. A computer readable medium storing a computer program which when executed places an online purchase order, the computer program for execution by a client device from which the purchase order originates, the computer program comprising: a set of instructions for downloading, at the client device, programming instructions for determining applicability of a discount type for the purchase order, the programming instructions being downloaded from a set of server computers connected to the client device through a network; a set of instructions for executing said downloaded programming instructions to determine the applicability of the discount type to the purchase order such that for multiple changes to the purchase order said programming instructions are executed at the client device multiple times to determine the applicability of the discount type without requiring new programming instructions to be downloaded through the network, said determining automatically done without human intervention and without downloading further instructions from the set of server computers; a set of instructions for receiving changes to the purchase order; a set of instructions for executing said downloaded programming instructions to determine the applicability of the discount type to the changed purchase order without downloading new programming instructions through the network; and a set of instructions for placing the online purchase order to the set of server computers through the network in accordance with the applicability of the discount type determined at the client device. 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.