Basic mapping support - IBM Mainframe

Basic mapping support (BMS) is an interface between CICS and CICS application programs that move 3270 datastreams to and from a terminal. BMS formats input and output display data in response to BMS commands and programs by using device information that is defined in the Terminal Definitions (WD) and the formatting information from the maps that were prepared for the application program.

In order to display a formatted screen, a terminal say IBM 3278, must receive a series of data stream called Native Mode Data Stream (NMDS), which is a mixture of Buffer control characters (BCCs) and text data, based on the hardware protocol. Since NMDS is designed for a particular terminal, it is both device dependent and format dependent. So if one is using NMDS he will have to re-code whenever there is a change in the terminal device or screen format, thus reducing the maintainability. In order to free the application program from the device and format dependency, CICS provides a facility called Basic Mapping Support (BMS).

The primary objective of BMS is to make the application program device and format independent. This is achieved by:

  • Removing the device dependent codes form an. application program and placing them in maps.
  • Removing constant information like titles, headers, etc., and placing them in maps.
  • Constructing the NMDS required to produce the desired screen.
  • Providing access to data fields of NMDS using symbolic names, which allow the repositioning of the fields without modifying the application program.
  • Providing text-handling capability.
  • Providing the Terminal paging facility, which allow the combination of several small mapped data areas into one or more pages of output.
  • Providing Message Routing facility that allows sending of messages to one or more terminals.

A screen defined through BMS is called a map. There are 2 types of maps: Physical and Symbolical. BMS map is nothing but a program written in assembler language and CICS provides a set of assembler macros, called BMS macros, for doing this.

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