CICS Transactions

Everything a user does in CICS is a transaction. You type a short code, CICS starts the right program, and your work gets done. Understanding transactions is the key to understanding CICS.

What is a transaction

• A transaction is a unit of work identified by a transid of 1 to 4 characters, for example MNT1.
• The user starts it by typing the transid on a blank screen, pressing a PF key, or selecting a menu option.
• CICS looks up the transid, finds the first program to run, and attaches a task for this execution.
• The transaction ends when the program issues EXEC CICS RETURN without a TRANSID option.

How transactions are defined

• Each transid is defined to CICS with the program it should start first.
• In modern CICS this is done online with the CEDA transaction (RDO):-
  CEDA DEFINE TRANSACTION(ORDR) PROGRAM(ORDRPGM) DESCRIPTION(ORDER ENTRY TRANSACTION)
• Note:- After defining, the definition must be installed (CEDA INSTALL) before the transid can be used.
• In old-style CICS the same mapping lived in the PCT (Program Control Table).

CICS-supplied transactions

• CEMT - master terminal: inquire on and control the CICS system.
• CEDA - define and install resources (transactions, programs, files) while CICS runs.
• CESN / CESF - sign on and sign off the region.
• CEDF - the execution diagnostic facility: a debugger for stepping through CICS programs.
• CECI - command interpreter: lets you test a single EXEC CICS command interactively.
• These transactions start with the letter C, which is the convention for CICS-supplied transids.

Life of a transaction

• User types the transid and presses Enter.
• CICS attaches a task and loads the first program.
• The program runs, using EXEC CICS commands to talk to the terminal and data.
• The program issues EXEC CICS RETURN - the task ends, or a new transaction starts if TRANSID was given.