Key Takeaways — Chapter 8: Paragraph and Section Design

Core Concepts

1. Top-down design is the foundation of structured COBOL programming. Start with the program's overall purpose in 1000-MAIN, decompose into major steps, and continue decomposing until each paragraph is small and single-purpose.

2. Every batch program follows the IPT pattern. Initialize-Process-Terminate structures virtually every COBOL batch program. Learn it, use it, teach it.

3. Paragraph names are the primary documentation. Verb-noun naming with hierarchical numbering communicates program structure without reading a single line of business logic.

4. High cohesion, low coupling. Each paragraph should do one thing (cohesion) and communicate with other paragraphs through clear contracts like 88-level condition names (low coupling).

5. Self-documenting code is not a luxury — it is a survival strategy. Programs live for decades. When a business analyst can read your paragraph names and verify correctness, you have achieved the gold standard.

Design Principles

• The Rule of 7: No paragraph should PERFORM more than ~7 subordinate paragraphs
• The Scroll Test: No paragraph body should exceed one screen (~25-50 lines)
• The Single-Sentence Test: If you need "and" to describe what a paragraph does, split it
• The Misleading Name Test: A paragraph that does more than its name implies is worse than a vaguely named paragraph

GO TO Decision Framework

Program Design Checklist

• [ ] 1000-MAIN follows IPT pattern
• [ ] Hierarchical numbering: 1000s (main), 2000s (processing), 3000s (detail), 9000s (error)
• [ ] All paragraphs use verb-noun names
• [ ] No paragraph exceeds 50 lines
• [ ] No nesting deeper than 3 levels within any paragraph
• [ ] 88-level condition names for all inter-paragraph communication
• [ ] Every EVALUATE has WHEN OTHER
• [ ] All END-IF, END-EVALUATE, END-PERFORM used (no period-delimited conditionals)
• [ ] Single entry, single exit for every paragraph
• [ ] Every paragraph is PERFORMed (no dead code)

Common Anti-Patterns