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CSD - CICS System Definition

Enhanced Definition

The CICS System Definition (CSD) is a VSAM Key -Sequenced Data Set (KSDS) that serves as the central repository for all CICS resource definitions. It stores the configuration details for programs, transactions, files, terminals, queues, and other components required for CICS regions to operate. Its primary purpose is to manage and activate these resources, enabling CICS applications to function.

Key Characteristics

- VSAM KSDS File: The CSD is implemented as a standard VSAM KSDS, allowing for efficient keyed access and updates to resource definitions.
- Centralized Repository: It consolidates all CICS resource definitions into a single, structured file, providing a consistent view across multiple CICS regions.
- Online and Offline Management: Resource definitions can be managed interactively using the CEDA online transaction or in batch mode using the DFHCSDUP utility program.
- Resource Groups and Lists: Definitions are organized into logical groups, and these groups are further organized into lists. CICS regions typically install one or more lists at startup to activate their required resources.
- Dynamic Updates: Many CSD definitions can be installed, modified, or discarded dynamically in an active CICS region without requiring a CICS restart.
- Shareable: A single CSD file can be shared by multiple CICS regions, facilitating consistent resource definitions across different environments (e.g., test, QA, production).

Use Cases

- Defining New Applications: Creating new PROGRAM, TRANSACTION, FILE, MAPSET, and other definitions for a newly developed COBOL application.
- Configuring CICS Regions: Specifying which GROUPs of resources a particular CICS region should install at startup via its System Initialization Table (SIT) parameter GRPLIST.
- Modifying Resource Attributes: Changing the STATUS of a TRANSACTION from ENABLED to DISABLED or updating the DSNAME of a FILE definition.
- Managing Terminal Connectivity: Defining TERMINAL and TYPETERM resources to allow users to connect to CICS from various terminal types.
- Implementing Security: Linking CICS TRANSACTION and PROGRAM definitions to external security manager (e.g., RACF) profiles for access control.

Related Concepts

The CSD is fundamental to the operation of any CICS region, as it provides the definitions that dictate what resources the region can use and how. It is managed by the CEDA transaction for online updates and the DFHCSDUP utility for batch processing, both of which interact directly with the CSD file. Resource definitions within the CSD are organized into groups and lists, which are crucial for managing the lifecycle and activation of resources within a CICS environment.

Best Practices:

Version Control: Treat CSD updates like source code changes; manage them through a robust change management system, especially for production environments.
Offline Updates for Production: Prefer using the DFHCSDUP utility for production CSD updates to ensure consistency, provide an audit trail, and minimize potential online errors.
Logical Grouping: Organize resource definitions into logical groups (e.g., by application, by environment, by function) to simplify management and deployment.
Backup and Recovery: Implement regular backup procedures for the CSD file to ensure quick recovery in case of data corruption or accidental deletion.
Thorough Testing: Always test CSD changes in non-production CICS regions before deploying them to production to prevent unexpected outages or application failures.