Chapter 12. Introduction to basic mapping support (BMS)
Basic mapping support (BMS) is an interface between CICS application programs and terminal devices, including printers.
A CICS application program can use BMS or terminal control commands to perform input and output. BMS has most of the facilities you need, and is easier to use than terminal control. However, you might sometimes need to use terminal control.
BMS lets you separate the tasks of display design and CICS application programming. It interprets generalized
device-independent
application program output commands, and generates
device-dependent
data streams for specific output devices. It also transforms incoming data streams to a form acceptable to application programs. BMS learns about the format of the data stream for the terminal from the terminal control table terminal entry (the TCTTE) for the task, not from the application program.
You can use the same BMS input or output commands in your application program to talk to different kinds of devices. A single BMS command in your program applies equally to various devices because BMS interprets commands differently for different device types.
BMS commands are quite simple, because all the low-level formatting information is held separately, in
maps
. This makes your application programs easier to write and less affected by changes to the system or its devices. You can change the layout of the information on the terminal device just by changing the map source and recreating the maps.
For the OS/400 programmer who is new to the concepts of the CICS family, BMS can be most easily described as similar to OS/400 data description specifications that would be used to describe a display image or printer file. See the DDS information in the Database and file systems topic in the iSeries Information
Center for DDS reference information and the
ADTS for AS/400: Screen Design Aid
manual for further details.
BMS definitions are held in members of a physical source file just like the source for any other high-level language program on the iSeries. There is a version of this physical source file called QMAPSRC which you can use as a sample for your BMS maps.
How BMS affects programming
Different versions of a display map can exploit the features of the IBM 3270 or IBM
5250 terminals. By having the screen data in
fields
(that is, defining data as having
field
format), you can address predefined fields in a display symbolically by name from within your application, without knowing the actual screen positions of those fields.
Changing field data to and from its displayable form is called
mapping
.
Although the same fields must appear in all versions of a display image, you can move them around in the different versions. This is useful when you’re
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