Abstract: A net market system, the net market system functioning as a portal for buying/selling and exchanging goods, information, and services via a network, that comprises net market system connection/management means that performs transmission and receptions of messages with the users via communication appliances, transactions monitoring means that monitors transactions within the net market system, data storing/providing means that stores data necessary for the execution of processing based on the messages from the users or that provides that data according to the requests made by the users' messages, application software providing means that provides application software that is necessary for the execution of processing based on the requests made by the users' messages, legacy-system interface providing means that provides an interface for having access to, or utilizing, legacy systems or software, and process-execution integrating/controlling means that integrates and controls the execution of processing within t