Business Rule

Enhanced Definition

A business rule is a statement that defines or constrains some aspect of a business, dictating how an organization operates, processes data, or makes decisions. In the mainframe context, these rules are typically embedded within application logic (e.g., COBOL programs) to enforce policies, validate data, and guide transaction processing according to specific organizational requirements.

Key Characteristics

- Embedded Logic: Traditionally, business rules on z/OS are implemented directly within procedural programming languages like COBOL, PL/I, or Assembler, residing in the PROCEDURE DIVISION of a program.
- Data-Driven: Many rules depend on specific data values (e.g., customer status, transaction amount, date) to determine the appropriate action or calculation.
- Conditional Execution: Rules often involve IF/THEN/ELSE constructs or EVALUATE statements to execute specific code paths based on predefined conditions.
- Maintainability Challenge: When rules are deeply embedded and scattered across large, monolithic applications, maintenance and updates can be complex and error-prone.
- Performance Critical: For high-volume transaction processing systems (e.g., CICS, IMS TM), the efficient execution of business rules is crucial for system performance and throughput.

Use Cases

- Credit Card Authorization: A CICS transaction program might apply rules to approve or decline a credit card transaction based on available credit, fraud detection scores, and merchant category codes.
- Payroll Calculation: A COBOL batch program calculates an employee's net pay by applying rules for tax deductions, benefits, and overtime based on salary, hours worked, and government regulations.
- Insurance Policy Premium Calculation: An application determines the premium for an insurance policy based on rules considering factors like age, location, claim history, and coverage options.
- Inventory Management: Rules define reorder points, preferred suppliers, and stock allocation logic within a DB2 or IMS DB application to optimize warehouse operations.
- Data Validation: Before updating a VSAM file or DB2 table, a program enforces rules to ensure data integrity, such as checking if a date is valid or a numeric field contains only digits.

Related Concepts

Business rules are fundamental to the functionality of most mainframe applications. They are the core logic that COBOL or PL/I programs execute, often triggered by JCL job steps in batch or by user interactions in CICS or IMS TM online environments. While traditionally hardcoded, modern approaches might involve Business Rule Management Systems (BRMS) or external configuration files to separate rules from application code, enhancing flexibility. DB2 and IMS DB can also enforce certain business rules through features like triggers, stored procedures, and constraints.

Best Practices:

Modularize and Isolate: Encapsulate related business rules into separate paragraphs, sections, or subroutines within COBOL programs to improve readability and maintainability.
Externalize Where Possible: For rules that change frequently, consider externalizing them into configuration files, DB2 tables, or leveraging a Business Rule Management System (BRMS) to reduce code changes.
Document Thoroughly: Maintain clear and up-to-date documentation for all business rules, explaining their purpose, conditions, and expected outcomes, especially for complex or critical logic.
Design for Testability: Write rules in a way that allows for easy unit testing and regression testing, ensuring that changes do not introduce unintended side effects.
Avoid Hardcoding: Minimize hardcoding of values that are subject to change (e.g., tax rates, thresholds); instead, store them in parameters, configuration files, or database tables.