Design overview

BMS is an interface between CICS® and its application programs. BMS formats input and output display data in response to BMS commands in programs. To do this, it uses device information from CICS system tables, and formatting information from maps that you have prepared for the program.

BMS enables an application program to read in device-dependent data and convert it to a device-independent standard form, or to generate device-dependent output data from this device-independent standard form. In both cases, the structure of the device-independent standard form, and the layout of the data on the display terminal, are determined by a user-defined map. Related maps—for example, maps used in the same application program—are grouped together into a map set. See Basic mapping support for further information about the definition and use of maps and map sets.

On some terminals (such as the IBM® 8775 display terminal and the IBM 3290 information panel), the available display area may be divided into a set of related “logical” screens called partitions. The layout and properties of the set of partitions that can be simultaneously displayed on a terminal are defined by the BMS user in a partition set. See Basic mapping support for further details about the definition and use of partition sets.

Maps, map sets, and partition sets are assembled offline using CICS macros. The user defines and names fields and groups of fields that can be written to and read from the devices supported by BMS. The assembled maps contain all the device-dependent control characters necessary for the proper manipulation of the data stream.

Associated with each map is a table of field names which is copied into each application program that uses the map. Data is passed to and from the application program under these field names. The application program is written to manipulate the data under the various field names so that alteration of a map format does not necessarily lead to changes in program logic. New fields can be added to a map format without making it necessary to reprogram existing applications.

Output data can be supplied from the application program by placing the data in the table under the appropriate field name. As an alternative, output maps can contain field default data that is sent when data is not supplied by an application program. This facility permits the specification of titles, headers, and so on, for output maps.

Optionally, the display of all the default data can be suppressed by the application program for any output map. Each time a map is used, the application program can temporarily modify the attributes of any named field in the output map. The extended attributes can also be modified if maps are defined with the DSATTS operand.

Output map fields with no field names can contain default data, but the application program cannot replace the default data or modify the attributes of unnamed fields.

For input, the user assembles a map defining the fields that can be written to and received from a particular device. Any data received for a particular field is moved across using the field name in the symbolic storage definition for the map. Light-pen-detectable fields defined in an input map are flagged as detected if present in an IBM 3270 Information Display System input stream. An input map for a particular case can specify a subset of the fields potentially receivable; any fields received and not represented in that map are discarded. This permits the number of fields from a map that can be typed or selected to be changed, without making it necessary to reprogram applications that currently receive data from the map.

Maps are stored in the CICS program load library. When a map is required by BMS, a copy is automatically retrieved by CICS from the program load library without application program action. Multiple users of a map contained in the program load library share a single copy in main storage.

BMS permits any valid combination of field attributes to be specified by the user when generating maps. Inclusion of BMS in CICS is a system generation option and does not prevent the application program from accessing a particular device in native mode (without using BMS). Intermixing BMS and native mode support for a terminal from the same application program may yield unpredictable results. When using mixed mode support, it is the user’s responsibility to ensure the correct construction and interpretation of native mode data streams.

BMS permits the application program to pass a native mode data stream that has already been read in, and (if, for a terminal of the IBM 3270 Information Display System, the screen has been formatted) to interpret this data stream according to a given input map. This facility allows data entered with the initial reading of a transaction to be successfully mapped using BMS.