CICS Overview and Functions
CICS is called as Customer Information Control System. The main functionality of CICS is it acts as an interface between the Operating System and application programs.
Functions of CICS
- Acts as interface between operating system and application programs.
- Does the function of data communication and therefore handle data. In other words CICS can support number of terminals or systems and acts as a data communication system between them.
- Take care of application program functions along with that take care of system functions also
- Also help in the task of monitoring
- Acts as a specialized operating system by providing environment for the execution of online application programs.
- CICS handles file management itself and so there is no need for statements like READ ,WRITE,OPEN
Before going into what CICS does and handles it would be easier if we get to know some common terminologies used with CICS namely Task and Transaction.
What is Task: This is defined as the fundamental unit of work which is scheduled by CICS namely to write to the workstation, read from workstation, read from a file, write to a file, initiate another task, call another function and so on.
What is a Transaction: This is one which commences the execution of a task. CICS assigns and identifies each transaction by a transaction identifier.
Having known about task and transaction let us see how both are handled together in CICS. We have seen above that when a transaction is started then it executes a task. But one may have a doubt whether CICS can handle more than one task at the same time for same transaction. The answer is yes. In other words if a transaction say tran1 is started or initiated more than one time again and again then CICS transaction tran1 create more than one task at the same time. This is how a task or more than one task gets created. Now we switch to see how to initiate a transaction which is essential for starting a task. There are many ways to start transaction let us see some of the ways of initiating or starting a transaction.
One of the ways could be to use a transaction identifier to initiate a transaction. This is because we have seen already that CICS assigns and identifies each transaction by a transaction identifier. So by entering the transaction identifier in the CICS screen and by pressing enter key CICS transaction associated with the transaction identifier entered gets initiated and invoked. It is also possible to initiate a transaction by using the CICS command START. This also provides the facility of starting a transaction after a specified time interval.
CICS also has the option of initiating a task automatically technically called as Automatic Task Initiation. One can initiate a transaction in this way also.