A financial transaction processing system (10) enables processing transactions from various types of card activated terminal devices (12) which communicate using a variety of electronic message formats. The transaction processing system may operate to authorize transactions internally using information stored in a relational database (32) or may communicate with external authorization systems (18). The transaction processing system includes among its software components message gateway routers (MGRs) (24, 164) which operate using information stored in the relational database to convert messages from a variety of external message formats used by the external devices and authorization systems, to a common internal message format used within the system. The system further uses database information to internally route messages to message processing programs (MPPs) (108, 138) which process messages and generate messages to the external devices and authorization systems. The MGR also converts the outgoing messages from the internal message format to the external message formats which can be interpreted by the external devices and systems to which the messages are directed.