Errors, Defects, Failures, and Root Causes

Errors

Mistakes made during the development process.

Remember that everyone is doing their best. Errors are unintentional. Everyone is human. Everyone makes mistakes. We can help them.

Defects

Flaws or malfunctions that deviate from the intended behavior or design.

Failures

Failures occur when the software does not perform its intended functions.

Root Cause

Identifies the underlying reason or source of a defect or failure.

Causes of software defects

• Humans are fallible
• Pressure
• Complexity

An error (mistake by human)
⬇️
Causes a defect/fault/bug (result of an error, e.g. someone coded it incorrectly)
⬇️
Causes a failure (system does not perform as expected, e.g. wages aren’t paid in 4 decimal places)

Other causes of failure

Failures can occur under environmental conditions (physical, not just infra).

Review Questions

What is the difference between a defect and failure?

Failure is identifying the software fails to meet it’s requirements.
A defect is is what was responsible for causing the failure.