CICS FAQ's

INTRODUCTION TO CICS 

  1.  1.  What is an online system?
Online system is a system in which the end user can interact with the system to get the information

Up to date files can be accessed by many users at a time
Data validation and editing can be done at the data entry time
Users can have the computer facility when needed

 A real rime system is an online system where the response time is minimal.

In a Batch processing system, transactions are accumulated into groups, or batches, before they are processed. For example the processing of the Orders collected for the whole day. In an Online processing system the transactions are processed by the system as soon as the transaction is entered on to the system. Ex. Airplane Reservation system. In a batch system the turnaround time is measured in hours and days, while for the On-line system it is measured in micro-seconds and seconds. On an Online system, if there is an error in data, the system indicates it immediately, and can be corrected and reprocessed. Allstate Insurance Co., uses CICS V4.1. on their system.

  5.    5.What are the four major types of Online Programs?
The menu program.
The inquiry program.
The file maintenance program.
The Data Entry program.

  6.    6.Describe the different considerations for the Online programs (CICS).
Ease of use. IBM promotes a user interface standard called CUA (common user Access). CUA provides Entry model, Graphical model, and Intermediate model - the text subset of graphical model.

Performance. Performance is a critical consideration for online programs. Performance for online systems is measured in terms of response time. Many factors affect response time. The most critical factors are the total number of programs running within the CICS system, the Disk I/O, the terminal and host computers and network.

File Integrity. A batch program typically has complete control of the files it uses, so there's no chance of another interfering with its processing. In an online system however many terminal users use the system simultaneously, and all must have access to the files they require at the same time.

Security. On batch systems Security implementation is simple as the access to the computer system can be controlled. However in an online system terminals are located at several locations. Logon procedure being used can ensure security to a great extent. Using of multi-level security to allow only certain users to access files and programs based on the logon id helps to secure the system.

  7.    7.What are the current CICS products?
CICS/MVS version 2 release 1
CICS/OS/VS version 1 release 7
CICS/DOS/VS version 1 release 7
CICS/VM release 2
CICS OS/2

  8.    8.How are the current CICS products different from each other?
The systems are compatible with certain exceptions caused by the differences among the corresponding operating systems      

  9.    9.What is a DB/DC system?
DB/DC stands for Database/Data communication system

10.   10. What are CICS control programs?
      FCP – File control
      JCP – Journal control
      KCP- Task control
      PCP- Program control
      SCP- Storage control
      TCP- Terminal control program
      TDP- Transient data program
      TSP-Temporary storage program

11.    11.Can we do a SORT by the SORT verb in a CICS program?
No

12.    12.What is Quasi-re-entrancy? Can you give examples of Quasi-reentrant programs?
A re entrant program is a program which will not get modified and which can renter into itself and continue processing after an interruption by the operating system. These programs are called re entrant programs in an OS environment and quasi re entrant programs in CICS environment.
For example, 50 users are using program A, CICS will provide 50 Working storage for that program but one Procedure Division.

13.  13.  How a CICS transaction can be initiated?
A transaction identifier and data are entered in a terminal. TCP with TCT recognises incoming data from the terminal. SCP acquires the storage for the terminal Input-Output Area (TIOA). TCP places the data from the terminal into TIOA and sets the pointer into the TCT entry of the terminal. If there is no task associated with the with this terminal, TCP passes control to KCP, Which realises the transaction in the data in TIOA.SCP acquires storage for the Task control Area, in which KCP prepares control data for this task. KCP, through PCT, tries to find the application program associated with the transaction. If PPT of the application program does not show the resident address of the program, KCP passes control to PCP, which fetches the application program from the load library and places it into the main storage. KCP passes control to the application program. The application program starts processing –the transaction has been initiated.

14.    14.How many ways can we initiate a CICS transaction? What are they?
There are 5 ways and are described below

1.By a transaction identifier entered in a terminal with Enter key. This is the most common way of initiating a CICS transaction.
When the Trans-id is entered on the CICS screen, it locates the program associated with the trans-id from the PCT. Then the location of the program is determined by CICS by reading the entries in PPT. After the load module is located, it loads it onto the CICS main memory, then task workspace is assigned for CICS own use to execute the task.
2.By a transaction identifier associated with a terminal for pseudo-conversation. This is a typical way of achieving a pseudo-conversation.
3.By the start command which initiates a transaction specified in the parameter.
4. By the Automatic Task Initiation (ATI). The destination control table (DCT) entry for an Intrapartition Transient Data Queue can have a trigger level parameter and the associated CICS transaction to be initiated if the trigger level is reached.
5.By a 3270 attention identifier. For the IBM 3270 type terminals, any of PF keys and PA keys could be identified in PCT to initiate a CICS transaction.

15.   15. What is pseudo conversation and how is it achieved in CICS programs?
Pseudo conversation is one in which a conversation is carried out by more than one task. It is achieved by quasi re-entrancy.

16.    16.What is the difference between conversation and pseudo conversation in CICS?
Conversational mode: In this mode, the program accomplishes a conversation by simply sending a message to the terminal, waiting for the user to respond, and receiving the response from the terminal. A program or transaction written in this mode is called the conversational program or transaction, respectively.

Pseudo conversational mode: In a Pseudo-Conversational program, a program attempts a conversation with a terminal user, it terminates the task after sending a message with a linkage for the next task. When the user completes the response the next task is automatically initiated. Pseudo-conversational program's uses the CICS resources such as control tables efficiently.But, from the user’s point of view, it looks like a normal conversation. A program or transaction written in this mode is called the pseudo-conversational program or transaction, respectively.

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