IMSDC- MFS 4 Control Blocks -Part 1 Posted on April 7, 2012 Exactly 2 years completed starting this blog. No where people getting correct info on IMSDC. I am trying to give good content on IMSDC. I hope it will be helpful. You know, in CICS, so many terminal control programs involved when you start a transaction. In IMSDC, 4 control blocks will be involved when you start a transaction. Source: IBM Message Output Descriptors (MODs)Define the layout of messages MFS receives from the application program. Device Output Formats (DOFs)Describe how MFS formats messages for each of the devices the program communicates with. Device Input Formats (DIFs)Describe the formats of messages MFS receives from each of the devices the program communicates with. Message Input Descriptors (MIDs)Describe how MFS further formats messages so that the application program can process them. We define these 4 control blocks in MFS macros. In the screen, when we enter /FORMAT PAYDAY1, first IMS locates MOD with the name PAYDAY1 , and displays a screen with this name. DOF decides, based on transaction code, and sends the required format of screen to the terminal. Means, what are the fields user should fill to get a response. More details refer my part-2. IMS DC-MFS Control Blocks-Part 2 Posted on April 10, 2012 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: Input message: 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.
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