BMS map

BMS, Basic Mapping Support, is how CICS applications define their screens. A map describes the layout: which text appears where, which positions are input fields, how long each one is, what colour and highlighting it has, and which are protected against typing.

The value is separation. The program does not build a screen character by character. It moves values into named fields and asks CICS to send the map, and CICS assembles the screen. On the way back, CICS hands the program the fields the user typed, already separated out.

That means the layout can be changed, by moving a field, relabelling it or adding highlighting, without touching the business logic.

Maps are written as source, assembled, and produce two outputs: the physical map CICS uses to build screens, and a symbolic map, a copybook of field definitions the program includes so it can refer to fields by name.

Modern CICS applications increasingly present themselves through web interfaces instead, but a very large number of screens still in daily use are BMS maps.