CICS Introduction

CICS is one of the most widely used online systems in the mainframe world. Almost every bank, airline and insurance company you know runs its day-to-day customer work on CICS.

What CICS stands for

• CICS stands for Customer Information Control System.
• It is a transaction processing system (also called a transaction server) from IBM.
• It runs on IBM mainframes under the z/OS operating system.
• CICS has been the standard way to run online mainframe applications since 1968.

CICS as a transaction server

• CICS sits between the users and the data, as shown in the diagram above.
• It receives requests from terminals and networks and passes them to application programs.
• It lets thousands of users work at the same time and gives answers in seconds.
• It stays up and running 24 hours a day, 7 days a week.
• Application programs are usually written in COBOL, PL/I, Assembler or Java and use special EXEC CICS commands.

Who uses CICS

• Banks - ATM withdrawals, balance enquiry, fund transfers.
• Airlines - ticket booking and seat reservation systems.
• Insurance companies - policy enquiry and claim processing.
• Retail chains - point-of-sale and stock enquiry systems.
• Government departments - citizen records and tax systems.

A first look at a CICS program

• A CICS program talks to the user with EXEC CICS commands instead of COBOL DISPLAY and ACCEPT.
• Below is a small skeleton of a CICS COBOL program. It shows a screen map and then returns control to CICS:-
  IDENTIFICATION DIVISION. PROGRAM-ID. CICSDEMO. DATA DIVISION. WORKING-STORAGE SECTION. 01 WS-RESPONSE PIC S9(8) COMP. 01 WS-COMMAREA. 05 WS-CUSTOMER-NUM PIC X(10). PROCEDURE DIVISION. EXEC CICS SEND MAP('DEMO1') MAPSET('DEMOMAP') ERASE RESP(WS-RESPONSE) END-EXEC. EXEC CICS RETURN TRANSID('DEMO') COMMAREA(WS-COMMAREA) LENGTH(LENGTH OF WS-COMMAREA) END-EXEC.
• Note:- SEND MAP displays the screen, and RETURN hands control back to CICS. Every command you will learn in this course follows this same EXEC CICS ... END-EXEC pattern.