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CICS Basic Terminology

Essential terms and concepts you need to understand when working with CICS transaction processing systems.

Foundation Concepts
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Introduction to CICS Terminology

CICS has its own specialized vocabulary that can be overwhelming for newcomers. Understanding these terms is essential for effective communication and system administration. This tutorial covers the fundamental concepts that form the foundation of CICS knowledge.

🎯Learning Objective

By the end of this tutorial, you'll understand the core CICS concepts including regions, transactions, programs, tasks, and the different types of conversational processing.

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Region

A CICS region is one of the most fundamental concepts in CICS architecture. Think of it as a self-contained environment where CICS runs and processes transactions.

What is a Region?

A CICS region is a separate address space that runs CICS and contains all the resources needed for transaction processing. It includes programs, files, terminals, and other resources that work together to process transactions.

💡Key Characteristics of a CICS Region

  • Separate address space from other regions
  • Contains its own programs and data
  • Manages its own resources
  • Processes transactions independently
  • Can communicate with other regions
  • Has its own security and recovery mechanisms

Transaction (TransID)

A CICS transaction is a unit of work that represents a complete business operation, such as checking an account balance or processing a payment.

What is a Transaction?

Each transaction has a unique transaction ID (TransID) and is processed by CICS programs. Transactions are the fundamental units of work in CICS systems.

🔍Transaction Examples

ACCT

Account inquiry transaction

PAYM

Payment processing transaction

XFER

Fund transfer transaction

MENU

Menu display transaction

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Program

A CICS program is the executable code that processes transactions. Programs contain the business logic and are written in languages like COBOL, PL/I, or Java.

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Task

A CICS task is the execution unit that processes a transaction. It represents a single instance of a transaction being processed.

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Conversational vs. Pseudo-Conversational

These are two different approaches to handling user interactions in CICS applications.

🔄Conversational Processing

  • Maintains connection throughout transaction
  • Program stays in memory
  • More resource intensive

Pseudo-Conversational Processing

  • Releases connection after each interaction
  • Program loads/unloads as needed
  • More efficient for high volume

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Reentrant, Quasi-Reentrant, Non-Reentrant Programs

These terms describe how programs handle multiple concurrent executions.

Reentrant Programs

Can be shared by multiple tasks simultaneously. Most efficient for high-volume applications.

⚠️Quasi-Reentrant Programs

Can be shared but with some limitations. Good balance between efficiency and complexity.

Non-Reentrant Programs

Can only be used by one task at a time. Least efficient but simplest to implement.

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Summary

Understanding these basic CICS terms is essential for working with CICS systems. These concepts form the foundation for more advanced topics in CICS administration and programming.

In the next tutorials, we'll explore how these concepts work together in CICS architecture and how to apply them in real-world scenarios.