Nature of bugs and preventive steps

Nature of bugs

A bug is a mistake that causes the software to behave differently from its specification. Bugs can be introduced at any phase:

• Requirement bugs: missing, wrong or ambiguous requirements.
• Design bugs: wrong algorithms, poor architecture, interface mismatch, ignoring timing or resource limits.
• Coding bugs: syntax and logic errors, uninitialised variables, wrong conditions, off-by-one, overflow, memory leaks, pointers, race conditions.
• Integration and environment bugs: module interface and compatibility problems.
• Maintenance bugs: changes that break existing features. Bugs can be permanent (always repeat) or transient/intermittent (depend on timing, input or environment, such as race conditions), and their cost increases if found late. Software bugs come from human error and complexity, not from wear.

Preventive steps

1. Clear requirements: document, review and get approval from the customer; maintain change control.
2. Good design: modular design, design reviews, use of proven patterns and models; simplicity.
3. Coding standards: naming, structured programming, avoid risky constructs, static code analysis tools.
4. Reviews and inspections: peer code review and walkthroughs at each phase.
5. Testing at every level: unit, integration, system and acceptance tests, regression tests after each change.
6. Defensive programming: input validation, error handling, assertions and watchdogs.
7. Configuration management: version control, build control and bug tracking.
8. Training, planning, adequate schedule and documentation, to avoid hasty coding.