An overview of MFS

MFS uses four kinds of control blocks to format messages between an application program and a terminal. The information you gather about how you want the data formatted when it is passed between the application program and the terminal is contained in these control blocks.

The two control blocks that describe input messages to IMS are:

• The device input format (DIF) describes to IMS what the input message is to look like when it is entered at the terminal.
• The message input descriptor (MID) tells IMS how the application program expects to receive the input message in its I/O area.

By using the DIF and the MID, IMS can translate the input message from the way that it is entered at the terminal to the way it should appear in the program's I/O area.

The two control blocks that describe output messages to IMS are:

• The message output descriptor (MOD) tells IMS what the output message is to look like in the program's I/O area.
• The device output format (DOF) tells IMS how the message should appear on the terminal.

To define the MFS control blocks for an application program, you need to know how you want the data to appear at the terminal and in the application program's I/O area for both input and output.