Programming requirements

Table 1 lists some of the considerations and questions that relate to writing a program operator. This list supplements the list of programming considerations found in Programming for the IBM 3270 Information Display System.

Table 1. Some considerations that affect the coding of a program operator
Program function	Programming considerations
Handling VTAM® operator commands and VTAM messages	Can a timer routine perform predefined actions while the network is active? How is the program operator going to examine and react to messages received from VTAM? Are there situations that require human intervention? Should displays be processed or reformatted prior to sending them to the terminal? Should commands be processed before sending them to VTAM? Are there other services that the program operator can provide? Operator-to-operator communication Hard-copy log (the hard-copy log available to the system console is not available to the program operator)
Opening the program operator	How many ACBs are to be opened? Are separate EXLSTs to be used if more that one ACB is used?
Establishing sessions to handle VTAM operator commands	When a terminal logs on, how is authorization for the terminal and the operator to be determined? Is the terminal or operator authorized to use the program operator? What type of authorization is to be used (for example, a password as a part of the logon message)? How does the program operator determine the terminal's authorization? Can this terminal receive all VTAM messages? Can this terminal enter only certain commands?
Correlating messages and responses	Is a table needed to associate messages and responses with a specific terminal? What type of messages are received by the program operator (solicited or unsolicited)? Note: The message-suppression level specified by the system console operator or a program operator determines the levels of VTAM operator messages received by any VTAM operator. How is the ID field of the header to be used? How is the header set up to send the message to VTAM? If a reply is requested, does the program operator Generate the reply? Pass the messages to a terminal? Keep track of the message until a reply is sent? If the terminal cannot receive the message, should it be sent to the system console, sent to another terminal, or discarded?
Outage of the session with the terminal operator	What happens to messages that are intended for the terminal? Should they be sent to the system console? Should they be sent to another terminal? Should they be discarded? If all the terminals are lost, what should the program operator do? Terminate? Request operator intervention? Wait for other terminals to log on?
Closing the program operator	In what order are the ACBs in the application program to be closed? Are outstanding messages to be sent to the system console? What happens if the first CLOSE fails? Should any additional messages be processed before issuing a second CLOSE?