The invention is directed to techniques for processing order messages exchanged between a client and an order server. The order messages can be for products and services that the customer orders from a vendor. The client provides the input order messages, which contain order commands in a predefined document format, to an order message manager of the order server, which also provides an order message sorter and message processing modules. The order message sorter reads the input document in the input order message to determine a type for the message and then directs the message to a message processing module capable of processing that type of order message. The message processing module processes the input document, obtains data if needed from an order database, and prepares an output document to include in an output order message to be returned to the client.