Custom
In the mainframe context, "custom" refers to software, configurations, or procedures that are specifically developed or modified to meet unique business requirements, extending or altering the standard functionality of IBM z/OS, its subsystems (like CICS, DB2, IMS), or third-party vendor products. It involves tailoring existing components or creating entirely new ones to fit an organization's specific operational needs.
Key Characteristics
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- Tailored Functionality: Designed to address specific business logic, data processing, or operational workflows not covered by off-the-shelf solutions.
- Integration with Core Systems: Must seamlessly interact with existing mainframe infrastructure, including z/OS, JCL, COBOL applications, databases (DB2, IMS), and transaction managers (CICS).
- Programming Languages: Often implemented using traditional mainframe languages such as COBOL, PL/I, Assembler, REXX, or C, compiled and executed within the z/OS environment.
- Configuration-Driven: Can involve modifying system parameters in
SYS1.PARMLIB,PROCLIB, or application-specific configuration files to alter behavior. - Maintenance Overhead: Requires dedicated resources for development, testing, documentation, and ongoing maintenance, especially during system upgrades or patches.
- Performance Sensitivity: Custom code must be written with mainframe performance considerations in mind to avoid impacting overall system throughput and response times.
Use Cases
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- Application Development: Creating bespoke business applications (e.g., payroll, inventory management, customer relationship systems) using COBOL or PL/I to run under CICS or as batch jobs.
- System Exits and User Exits: Implementing custom logic within IBM or vendor software exit points (e.g., security exits, data transformation exits, program control exits) to modify standard behavior.
- JCL Procedures (PROCs): Developing reusable, parameterized JCL procedures (
PROCs) to standardize and automate complex job streams for specific business processes. - Reporting and Analytics: Building custom reports and data extraction utilities using COBOL, SAS, or REXX to analyze data from DB2, IMS, or VSAM datasets.
- Security Rule Customization: Defining granular security rules and policies within RACF, ACF2, or Top Secret to control access to custom applications and data.
Related Concepts
Customizations are fundamental to how organizations leverage the mainframe's power, often building upon standard components like z/OS, JCL (to execute custom programs), COBOL or PL/I (for application logic), and interacting with CICS, DB2, or IMS for transaction processing and data management. They are typically managed through Source Code Management (SCM) systems like Endevor or CA-Librarian and are subject to rigorous Change Management processes to ensure system stability and integrity.
- Thorough Documentation: Document all custom code, configurations, and procedures comprehensively, including design specifications, change logs, and operational instructions.
- Version Control: Utilize robust mainframe-specific SCM tools to manage custom source code, JCL, and configuration files, ensuring proper versioning and rollback capabilities.
- Rigorous Testing: Implement a multi-stage testing strategy (unit, integration, system, regression) for all custom components to ensure stability, performance, and correctness before deployment.
- Performance Optimization: Design and code custom solutions with mainframe performance best practices in mind, optimizing CPU usage, I/O operations, and memory consumption.
- Security Review: Conduct regular security reviews of custom code and configurations to identify and mitigate potential vulnerabilities, adhering to enterprise security policies.
- Minimize Customization: Evaluate the necessity of each customization; simpler, less customized solutions are generally easier to maintain and upgrade.
- Adherence to Standards: Follow established coding standards, naming conventions, and architectural patterns to promote consistency and maintainability across the mainframe environment.