In Windows, you double-click a Program, to start it in the Online-Mode. However, in CICS, a user cannot directly start a Program. Instead, you define a Transaction, which in turn will run the COBOL Program in Online Mode. Every transaction has a 4-byte Unique identification number called Transaction ID. You wanna to run COBOL Programs in Online mode on CICS, transactions are the way.
How do you run a COBOL Program on CICS? On a CICS Terminal(like a Web-browser), when you type the Transaction-ID, and hit ENTER, the COBOL Program is loaded, immediately started in the online-mode. This is called invoking the Transaction. For example, if the COBOL-online Program is BOOKTKT, and the Transaction-ID is TBOOK, when you type TBOOK, and hit ENTER, CICS Software will find the the COBOL Program BOOKTKT on the Disk, and Load into the CICS Region and execute it in Online Mode. Similar to TSO, CICS Software serves many users simultaneously. CICS is a very robust Transaction Monitor (keeps listening for transactions) – it can handle trillions of transactions at a time.
When you invoke a transaction, by typing say TBOOK, it starts a COBOL Program like BOOKTKT. But how does the CICS Software, which COBOL Program to start for the transaction TBOOK? Moreover, the CICS Software also needs to know the place(location) to look for your COBOL Program. What is the PDS, Folder or library on the Disk in which the COBOL Load Module BOOKTKT resides, so that CICS Software can pick up the Load, and start running it. Now, all this extra-information is stored in CICS Tables.
The important CICS Tables are :
PCT – For Transactions
PPT – For COBOL Programs
FCT – For Files
RCT – For DB2 Connections
When you type the Transaction ID – TBOOK, on the Terminal, the CICS Software will look-up the Transaction in the PCT.
| Transaction |
Program |
| TBOOK |
BOOKTKT |
| TABC |
PROGR01 |
| TDEF |
PROG02 |
| ... |
... |
PCT Table(Program Control Table) tells the COBOL-CICS Program for any Transaction.
| Program |
Load Pointer |
| BUA21 |
AGY0157.CICS.LOADS |
| BUA22 |
AGY0157.CICS.LOADS |
| BOOKTKT |
AGY0157.DEMO.CICS.LOADLIB |
| BUA23 |
AGY0157.DEMO.CICS.LOADLIB | PPT Table(Process Program Table) tells the location(Load Library) from which the COBOL Program(Load) must be picked up, and loaded into the CICS Region
|