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BMS receives the data entered by the user and then formats it into a symbolic map area. The application program has access only to the data present in the symbolic map. The application program processes the data and the output is sent to the symbolic map. BMS will merge the output of the symbolic data with the physical map.

Physical Map

Physical Map is a load module in the load library which contains information about how the map should be displayed.

• It contains the details about the attributes of all the fields in the map and their positions.
• It contains the display format of the map for a given terminal.
• It is coded using BMS macros. It is assembled separately and link edited into the CICS library.

Symbolic Map

A Symbolic Map is a Copy book in the library. The Copy book is used by the CICS application program to send and receive data from the terminal.

• It contains all the variable data which is copied into program’s WORKINGSTORAGE section.
• It has all the named fields. The application programmer uses these fields to read and write data into the map.

Skipper and Stopper Field

For an unprotected named field, in a map, if we have specified a length of 10, this means that the name field can take values whose length cannot exceed 10. But when you display this map using CICS and start entering values for this field on the screen, we can enter more than 10 Characters, i.e., till the end of the screen and we can enter even in the next line. To prevent this, we use Skipper field or stopper field. A Skipper field would generally be an Unnamed field of length 1, specified after a named field.

Skipper Field

If we place a skipper field after the named unprotected field, then while entering the value, once the specified length is reached, the cursor will automatically position to the next unprotected field. The following example shows how to add a skipper field −

NUMBER  DFHMDF POS = (01,01), X
   LENGTH = 5, X
   ATTRB = (UNPROT,IC)
      DFHMDF POS = (01,07), X
      LENGTH = 1, X
      ATTRB = (ASKIP)

Stopper Field

If we place a stopper field after the named unprotected field, then while entering the value, once the specified length is reached, the cursor will stop its positioning. The following example shows how to add a stopper field −

NUMBER  DFHMDF POS = (01,01), X
   LENGTH = 5, X
	ATTRB = (UNPROT,IC)
	   DFHMDF POS = (01,07), X
      LENGTH = 1, X
      ATTRB = (PROT)

Attribute Byte

The attribute byte of any field stores information about the physical properties of the field. The following diagram and the table explain the significance of each bit.

Modified Data Tag

Modified Data Tag (MDT) is the last bit in the attribute byte.

• MDT is a flag which holds a single bit. It specifies whether the value is to be transferred to the system or not.
• Its default value is 1, when the field value is changed.
• If MDT is 0, then data cannot be transferred; and if MDT is 1, then data can be transferred.

Send Map

The send map command writes formatted output to the terminal. It is used to send the map to the terminal from the application program. The following code segment shows how to send a map to the terminal −

EXEC CICS SEND 
   MAP('map-name')
   MAPSET('mapset-name')
   [FROM(data-area)]
   [LENGTH(data_value)]
   [DATAONLY]
   [MAPONLY]
   [CURSOR]
   [ERASE/ERASEAUP]
   [FREEKB] 
   [FRSET]
END-EXEC   

The following table lists the parameters used in a send map command along with their significance.

Receive Map

When we want to receive input from a terminal, we use the RECEIVE MAP command. The MAP and MAPSET parameters have exactly the same meaning as for the SEND MAP command. The following code segment shows how to receive a map −

EXEC CICS RECEIVE 
   MAP('map-name')
   MAPSET('mapset-name')
   [INTO(data-area)]
   [FROM(data-area)]
   [LENGTH(data_value)]
END-EXEC

Mapset Execution

The following steps are necessary to develop and execute a mapset −

• Step 1 − Open a TSO session.
• Step 2 − Create a new PDS.
• Step 3 − Code a mapset in a new member according to the requirement.
• Step 4 − Assemble the mapset using the JCL provided by the CICS administrator.
• Step 5 − Open a CICS Session.
• Step 6 − Install the program using the command −CEMT SET PROG(mapset-name) NEW
• Step 7 − Type the following command to send the Map to the terminal −CECI SEND MAP(map-name) MAPSET(mapset-name) ERASE FREEKB