cics overview session

Asias Largest Global Software & Services Company

Ver 2.0

Customer Information Control

System (CICS)

Day 1 Session 1

Updated in Nov 2004


Ver 2.0

Course Objectives

After completing this course you should be able to

Appreciate the salient features of CICS as a Transaction Processing system and as a DB/DC System

Create user interfaces using CICS Basic Mapping Support (BMS).

Access and modify VSAM files, database tables.

Handle normal and abnormal CICS exception conditions.

Use advanced features of CICS: Data Tables, Intercommunication, etc.


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Sessions Outline

CICS Overview

CICS - Application Programming Considerations

CICS - Screen Handling - Basic Mapping Support

CICS - Error and Exception Handling

CICS - File and Database Handling

CICS - Program Control

CICS - Queuing Facility

CICS - Interval &Task Control

CICS - Testing and Debugging


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Sessions Outline Advanced Topics

CICS - Storage Control

CICS - CICS Intercommunication

CICS - Restart and Recovery

CICS - Administration and Set-up

DB2-CICS - Case Study


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CICS - Overview

Session 1


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Session 1 : Objectives

To Understand the Business requirements for an online transaction processing

environment

Features and Strengths of CICS

CICS Interface and Languages available to access CICS

CICS Concepts and Terminologies

Transaction Flow


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Batch System Online System

Batch System

Online System

Transaction file

MASTER FILE

REPORTS VSAM / DATABASE

Terminals

Batch and Online System


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An Online System

ONLINE processing allows a user to interact with a

computer and access its resources via a terminal

Example : Railway Reservation system

Sales Processing system

Costing system

Stock Clearing System


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What is CICS ?

Stands for Customer Information Control System

A world-class transaction processing system - by IBM in 1960s

Availability Four versions in OS/390, CICS Transaction server 2.1 in z/OS

AS/400, RISC/6000 & OS/2

PC Servers

Provides an interface between application programs and operating system services, such as data access and communication access


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CICS Interface


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CICS Concepts CICS runs as a batch job and can handle hundreds of interactive users

that are using a variety of applications

More than one CICS system (or region) can run on the same computer at the same time.

Programs running in one region do not interfere with programs running in another region


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Transactions and Tasks

CICS locates a application program using a four character code called Transaction-identifier

Application programs are associated with a transaction which when invoked starts a Task

A task is the execution of an application program for a specific user

Several users may invoke the same transaction, with each given a separate task


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Transactions and Tasks

TASK 1 TASK 2

TXNA TXNA

working

storage for

task 1

working

storage for

task 2

TASK 1 started at terminal1 by user1

executes TXNA.

TASK 2 started at terminal2 by user2

executes the same TXNA.

These two tasks use the same load

module associated with TXNA.

However, the working storage for

each task is different.


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Features and Strengths of CICS

Multitasking within a single address space provided by the Operating System

Multithreading allowing one copy of program loaded and shared by all users

Reentrancy of programs providing separate copy of working storage for each Task

Quasi-re-entrant

Priority handling


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CICS User Interfaces

Majority of CICS applications written for 3270 display terminals or PCs that are emulating 3270 terminals

Presentation and Business logic provided by CICS

the user interface is implemented using Basic Mapping Support (BMS)

CICS can also be used with other types of user interfaces CICS at the back-end provides business logic

Front end provides presentation logic

A VB program

A front-end program written in another platform

Web applications run in a Web browser through HTTP


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CICS Programming Languages

COBOL Most used in mainframe

Assembler language Fairly popular till 1970s

PL/I Alternative to COBOL in 1970s & 1980s

C and C++ Object oriented classes can be developed that access CICS services

Java Newest language for writing CICS applications

Object oriented classes can be developed that access CICS services


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System services

Monitoring functions

Application program

services

CICS System

Operating System ( MVS/ESA) Database

Access

Method (DL/I,

DB2)

Data

Access

(VSAM/

BDAM )

Telecommunication

Access method

(VTAM,TCAM,BTAM)

CICS/MVS

Data

handling

functions

Data

Storage Data communication

functions

CICS APP PROGRAMS (Cobol, PL/I, Assembler)

Terminal

Other systems


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CICS - Terms and Definitions

Logical Unit of Work (LUW)

Synchronization Point (Syncpoint)

Basic Mapping Support

Transaction Types


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Logical Unit of Work (LUW)

From the application designer's point of view, a LUW is a

sequence of actions that needs to be completed before any of

the individual actions can be regarded as complete as shown

below

- - - - - - - - - - - - - - - LUW - - - - - - - - - - - - - - -

Task A |----------------|---------------------|---------------------------

SOT Update Delete EOT

File - 1 2 records (SP)


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Synchronization Point (Synchpoint)

CICS automatically issues a SYNCPOINT at the end of

each task

All the updates made by the task so far will be committed

All the resources maintained by the dynamic log will be

released


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BMS

Interface between the application program and the terminal control (3270 devices)

Consists of supplied BMS modules and user-defined screen maps

Provides format independence which simplifies positioning of data on terminal

Uses maps as requested by the application program to control the formatting of terminal I/O data

Maps created using the online tool SDF/CICS


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CICS Application Pgm Communication


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Transaction Types

Conversational Program

Program (transaction) remains idle when waiting for

user response

Program, data areas, control blocks remain in main

storage resulting in high virtual storage utilization

Pseudo-conversational Program

Program ends after it sends data to a terminal

Program is in storage only when processing data,

otherwise storage released for other transactions/tasks.


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Transaction Types (Contd.)

Non-Conversational Program Programs (transactions) that are executed without user

intervention

Examples : Automatic Task Initiator, Batch Jobs


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CICS Sample Screen Customer

Inquiry


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Structure Chart of a Customer

Inquiry Program


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Conversation Type - Illustration

EXEC CICS SEND

SEND MAP(map_name) MAPSET(mapset_name)

FROM(data_area)

END_EXEC.

IF CONVERSATION-TYPE = CONVERSATIONAL THEN

EXEC CICS RECEIVE

MAP(map_name) MAPSET(mapset_name)

INTO(data_area)

END_EXEC

END-IF

EXEC CICS RETURN

TRANSID(txn_name)

END_EXEC.


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CICS Transaction Flow


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CICS- Control Programs and Tables

(IBM Supplied)

CIC

S

File

Control

(FCP)

Program

Control

(PCP)

Task

Control

(KCP)

Journal

Control

(JCP)

Terminal

Control

(TCP) Transient

Data

(TDP)

Temporary

Storage

(TSP)

Storage

Control

(SCP)


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CICS Control Programs & Tables

(User Specified)

Terminal Control Program - TCT Task Control Program - PCT Program Control Program - PPT File Control Program - FCT Resource Control Program - RCT Journal control Program - JCT Temporary Storage Program - TST Transient Data Program - DCT Storage Control Program - SCT


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Terminal Control Flow (TCT)

The Terminal Control

Table (TCT) has an entry

for each terminal

Together with Basic

Mapping Support,

terminal control provides

an application program,

the ability to communicate

with a terminal


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Task Control (PCT)

Task control validates transactions by checking the Program Control Table (PCT)

Task is created after the transaction is validated

Concurrent processing of more than 1 task is possible (multitasking)

Error message is sent to the terminal by task control for an invalid transaction


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Program Control (PPT)

Task Control passes control to Program Control, which keeps track of the location of every application program

The Processing Program Table (PPT) contains the program size, program source language, and other program information

Stores the program library address the first time to make subsequent loading of program faster


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User Application Programs

The application program processes the input and

issues commands to request services that are

needed in performing the function of the

application


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File Control and Database

The application program issues a command to retrieve a record from a VSAM file

VSAM/(B)DAM are the only files used in CICS and they should be defined in the File Control Table (FCT)

For access to relational database as DB2, define the attachment to DB2 in the Resource Control Table (RCT)


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Journal Control

The Journal control facility automatically logs the changes on the system log, when an application changes record in a file

System log defined in the Journal Control Table (JCT) enables CICS to back-out changes when a task fails

Maximum of 99 journals


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Trace Control

Tracing is a CICS debugging aid

CICS can write trace entries in a Trace Table (TRT)

Execute Diagnostic Facility (EDF) is another feature that enables interactive debugging

Command Interpreter (CECI) allows a programmer to enter and test CICS commands at the terminal directly


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Dump Control

In case of serious error

conditions, CICS will

abend the task with a task

dump

The CICS transaction

ABEND message

contains the ABEND

code.


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Temporary Storage Control

Controls storage of data in main storage or on disk for later retrieval

Records can be retrieved in the same sequence in which they are stored

Records reside in Temporary Storage Queue (TSQ) unless deleted or when CICS closes

Temporary Storage Table (TST) is required for recovery purpose


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Transient Data control

CICS queuing function sequential queue

The Destination Control Table (DCT) contains the queue definitions

Transient data has 2 types of queue: Intra-partition transient data

Extra-partition transient data


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Ending the transaction

Output of a CICS process Program extracts necessary fields from the VSAM record and setup

an output area to be sent to the terminal

Task ends when the application program issues the RETURN command

All storage associated will be released

Other tasks can use the storage just released


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Starting a TASK

TXN1 Trans. Program TXC1 MAPPGC1

TXC2 MAPPGC2

TXN1 TXNPGM1

TXN2 TXNPGM2

PCT

Program. Location

MAPPGC1 In Storage

MAPPGC2 On Disk

TXNPGM1 In Storage

TXNPGM2 On Disk

PPT

Load Module Library

MAPPGC1 MAPLIB

MAPPGC2 MAPLIB

TXNPGM1 PGMLIB

TXNPGM2 PGMLIB

CICS Address Space

TXNPGM1

MAPPGC1


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CICS System Responsibilities

Systems Programmer

Operators (Administrators) Application Programmer

IT Management


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Session 1: Summary

Overview of Online transaction processing environment

CICS Terms and Definitions

Transaction, task, LUW, conversational and

pseudo-conversational style

CICS control programs and control tables

CICS System Responsibilities


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References Yukihisa Kageyama, CICS Handbook, McGraw Hill Book

Co.

CICS/ESA Application Programming Guide, Ver.3, Release 2.1.

CICS/ESA Intercommunication Guide

Joseph Le Bert, CICS Made Easy, McGraw Hill International Editions, 1987

Raul Menendez and Doug Lowe, CICS for the COBOL Programmer, Part 1&2, Mike Murach & Associates, 1992

cics overview session

Documents