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optional · CSS study notes

System Delivery and Maintenance

CSS CS Optional — Paper-I, Section-B, Topic V.

🔑 System Delivery

  • Deployment planning: staged rollout vs "big bang"
  • Data migration from old system
  • User training
  • Documentation handover
  • ⚠️ No rollback plan → minor bug becomes an outage.

📌 Maintenance — 4 Types (memorize verbatim)

  • Corrective — fix bugs found after release.
  • Adaptive — adjust to changed environment (new OS/hardware/regulation).
  • Perfective — improve performance / add requested features.
  • Preventive — refactor/re-engineer before problems occur.

📌 Why Maintenance Is Most Expensive SDLC Phase (60–80% of lifetime cost)

  • Longest duration (years/decades)
  • Accumulated complexity ("software entropy"/"code rot")
  • Lost context (original devs move on)
  • Regression risk (every change needs re-testing)

🔥 Past Papers

  • 2026 Q6(a) — why is maintenance the most expensive phase? (name all 4 types)

⚠️ MCQ Trap

  • New data-protection law → adaptive (environment changed), not corrective/perfective.

📜 Past-Paper Questions & MCQs (CSS 2016–2026)

2026 · Paper-I · Q6(a) · 6 marks

Q. Why is maintenance the most expensive phase of the software lifecycle?

Ans.

  • It lasts the longest. Software is used for years or decades, while development takes months. Maintenance typically takes the majority of total lifetime cost (often quoted as 60–80%).
  • It covers four activities: corrective (fixing bugs), adaptive (new platforms or laws), perfective (new features and improvements) and preventive (cleaning up code).
  • Understanding old code is costly, especially when documentation is poor or the original developers have left.
  • Changes cause ripple effects, so extensive regression testing is needed.
  • Structure degrades with each change (software entropy), which makes later changes harder.
  • Ageing technology needs rare skills and old tools, and users keep requesting new features.
  • 2025 MCQ on refactoring is on Software Evolution.