High Level Language - HLL programming

Enhanced Definition

High Level Languages (HLLs) in the mainframe context are programming languages that provide a strong abstraction from the underlying hardware architecture, allowing developers to write code using human-readable syntax closer to natural language. They are compiled into machine code for execution on z/OS, significantly enhancing programmer productivity and application maintainability compared to low-level languages like Assembler.

Key Characteristics

- Abstraction from Hardware: HLLs abstract away the intricate details of the z/Architecture instruction set, memory management, and register usage, allowing programmers to focus on business logic rather than machine specifics.
- Readability and Maintainability: Their syntax is designed to be more intuitive and self-documenting, making code easier to understand, debug, and maintain over long periods, which is crucial for large enterprise applications.
- Relative Portability: While often compiled for a specific platform (z/OS), the source code itself can be more easily adapted or recompiled for different environments compared to platform-specific Assembler code.
- Requires a Compiler: HLL source code must be translated into executable machine code by a specific compiler (e.g., IBM Enterprise COBOL for z/OS, IBM XL C/C++ for z/OS) before it can run on the mainframe.
- Enhanced Productivity: By reducing the amount of code needed to perform complex operations and simplifying development, HLLs drastically improve development speed and reduce error rates.
- Common Examples on z/OS: COBOL, PL/I, C, C++, Java, REXX, and Python are prominent HLLs used for various application types on the z/OS platform.

Use Cases

- Business Application Development: COBOL remains the predominant HLL for developing and maintaining critical business applications, such as financial systems, insurance processing, and inventory management on z/OS.
- System Programming and Utilities: Languages like C and PL/I are frequently used for writing system utilities, performance monitors, and specialized system-level programs that require closer interaction with z/OS services.
- Transaction Processing Systems: COBOL and PL/I programs are extensively used within CICS (Customer Information Control System) and IMS TM (Information Management System Transaction Manager) for high-volume online transaction processing.
- Database Application Development: HLLs like COBOL, PL/I, and Java are used to develop applications that interact with DB2 for z/OS and IMS DB, embedding SQL or DL/I calls for data manipulation.
- Modernization and Integration: Java, Python, and Node.js (via z/OS Unix System Services) are increasingly used to develop new applications or integrate existing mainframe data and logic with modern web and cloud environments.