Refer my part-1 if you miss it. This post I am just explaining how these 4 control blocks align together.
When data entered on the screen, MID and DIF control blocks translate the data in the way IMS program understands. I hope so far my explanation has given good understanding on the 4 control blocks.
Let us see an example:
PAYDET FIRST LAST EMPID
Here “PAYDET” is the transaction code
FIRST==> First Name
LAST==> Last Name
EMPID==> Employee ID, however, from which logical terminal this message is coming will not appear in the message, but it will be captured in the first field of I/O PCB mask.
Example of output message:
LLZZFIRST LAST XXXXXXXXXXXX
Here, LL ==> length of the message PIC S9(4) Comp if it is in COBOL.
If PL1 is there it is PIC S9(8) Comp.
ZZ ==>2 byte field MFS formatting option.