What is a Transaction?

A transaction is the basic unit of work in CICS. Everything a CICS user does online happens inside a transaction.

A transaction is one complete business action

• A transaction is one complete piece of work, like adding a customer, enquiring a balance, or booking a ticket.
• It starts when the user types a transaction id and ends when CICS shows the final response.
• To the user it feels like one job, even if the program shows two or three screens in between.
• Example: “Add a new customer” is one transaction even though it uses a key map and a data map.

Online transactions vs batch jobs

• Online transactions run under CICS and talk to the user screen by screen.
• Batch jobs run through JCL with no user waiting at a screen.
• An online transaction must answer fast — usually within a couple of seconds.
• Each transaction is small and independent, so hundreds of users can run transactions at the same time.
• If one transaction fails, other users and their transactions are not affected.

How a user starts a transaction

• The user clears the terminal screen and types the 1-to-4 character transaction id.
• Pressing ENTER sends the id to CICS, which starts the matching program.
• A transaction can also be started by another program, by a menu option, or automatically at a scheduled time.
• Example of starting a transaction from a clear screen:-
  
  *--- A user starts a transaction by typing its id on a clear screen ---* MNT1 <-- transaction id of the customer maintenance program <press ENTER>