Explicit-mode client program logic flow

When the client requests the services of an explicit-mode server, the only protocol imposed by IMS TCP/IP is that the client must begin by establishing TCP/IP connectivity and sending a transaction-request message (TRM).

The Listener uses contents of the transaction-request message (TRM) to determine which transaction to schedule. If the request is not accepted (for example, because of failure to pass the security exit, or because the transaction was stopped by the IMS master terminal operator), the Listener returns a request-status message (RSM) to the client with an indication of the cause of failure. (See Request-status message segment for the format of the request-status message).

Once an explicit-mode client and server are in communication, there is no predefined input/output protocol. Rules of the conversation are established by agreement between the two programs. Any number of READ/WRITE calls can be issued. Upon termination, the server program should commit any database changes, notify the server of successful completion, and close the socket.

It is suggested that, when all database updates have been committed, the server notify the client by sending a success message to the client. This notifies the client that the transaction has completed properly and that all database updates have been committed. Unless such a message is sent, the client has no way of knowing that the transaction completed properly.