CAIE 9618 · Paper 2 · Topic 2.5.3

Software Maintenance
& Documentation

Corrective · Adaptive · Perfective · Internal & External Documentation

CSZone Cambridge International AS & A Level Computer Science 9618

Types of Software Maintenance

Three Types — Know Them All

After software is deployed, it must be maintained throughout its lifetime. The Cambridge spec defines three types:

Corrective

FIX BUGS

Fixing errors discovered after release. The software does not do what it was supposed to do. Bug was present at deployment but not caught during testing.

E.g. Tax calculation producing wrong result; login page crashes on Safari

Adaptive

ADAPT TO CHANGE

Modifying software to work in a new or changed environment. The environment has changed — not the software's fault. Also includes changes to meet new regulations.

E.g. Updating app after iOS 18 release; updating tax rates after new legislation

Perfective

IMPROVE

Adding new features or improving performance beyond the original spec. Software works correctly but is enhanced to meet user requests or improve efficiency.

E.g. Adding dark mode; optimising database queries to reduce load time

Internal Documentation

Documentation Inside the Code

Internal documentation is embedded within the source code itself, aimed at programmers working on or maintaining the code.

TYPES OF INTERNAL DOCUMENTATION

Inline comments — explaining what a block of code does (not how — the code shows how)

Meaningful identifiers — variables/procedures named clearly (e.g. calculateTotal not ct)

Indentation and structure — consistent formatting for readability

Header blocks — procedure/function descriptions, parameters, return values

// Calculate VAT on an amount
// Parameters: amount (REAL), rate (REAL)
// Returns: VAT amount (REAL)
FUNCTION calculateVAT(amount : REAL, rate : REAL) : REAL
// Rate passed as decimal (e.g. 0.20 for 20%)
RETURN amount * rate
ENDFUNCTION

Benefit: Enables programmers to understand, debug, and maintain code without needing to contact the original author.

External Documentation

Documentation Outside the Code

External documentation exists as separate documents. It targets different audiences at different stages of the software life cycle.

TECHNICAL DOCUMENTATION (for developers)

System specification — overall architecture

Data dictionary — all variables and their types

Data flow diagrams, entity-relationship diagrams

Algorithm design documents, pseudocode

Test plan — all tests, expected results, actual results

USER DOCUMENTATION (for end users)

User manual — how to install and use the software

Quick start guides and tutorials

Troubleshooting FAQ

Online help system / tooltips

MAINTENANCE DOCUMENTATION

Guides for future maintainers — known issues, change history, version notes, module dependencies.

Why Documentation Matters

Documentation Enables Maintenance

WITHOUT DOCUMENTATION

Maintainers must reverse-engineer the code to understand it

Risk of accidentally breaking working features when fixing bugs

Increased cost and time for every change

Knowledge lost when original developer leaves

WITH GOOD DOCUMENTATION

New developers understand system quickly

Corrective maintenance faster — root cause easier to find

Adaptive maintenance safer — dependencies documented

Perfective maintenance planned — architecture understood

Users can troubleshoot independently using the user manual

Exam Practice

Cambridge-style questions

Question 1

A company's payroll software was updated to handle a new pension scheme introduced by the government. State the type of maintenance carried out and give a reason for your answer. [2]

1

Adaptive maintenance.

1

Because the software was modified to accommodate a change in external requirements (new government legislation), not to fix a bug or add a feature requested by users.

Question 2

Explain why good documentation is important when carrying out software maintenance. [2]

Common Mistakes

Don't lose easy marks

1

Confusing corrective and adaptive — corrective = a bug was found (software behaved incorrectly). Adaptive = environment changed (new OS, new law, new hardware). A common trap: "updating the app for Windows 11" is adaptive not corrective — no bug was present.

2

Saying "documentation helps users" as the only benefit — in a maintenance question, the examiners want you to say documentation helps programmers/maintainers understand the system, find bugs faster, and make changes without breaking other parts. User documentation is secondary in this context.

3

Giving internal documentation examples for external documentation or vice versa — internal = inside the code (comments, meaningful identifiers, indentation). External = separate documents (user manual, technical spec, test plan, data dictionary). Never mix the two in the same answer.

Topic Summary — 2.5.3

What You Need to Know

MAINTENANCE TYPES

Corrective — fix bugs discovered post-release
Adaptive — adapt to changed environment/law
Perfective — improve features/performance

REMEMBER

Maintenance occurs after deployment. Most software spends more time being maintained than developed — hence documentation is critical.

DOCUMENTATION

Internal: comments, meaningful names, indentation, header blocks
External (technical): system spec, data dictionary, test plan, DFDs
External (user): user manual, quick start, FAQ, help system

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