Unit 4: Quality and release management

Software quality is conformance to explicit requirements, standards and implicit expectations. It has two views: quality of design and quality of conformance. Cost of quality: prevention costs (training, planning), appraisal costs (reviews, testing) and failure costs (internal — before release; external — after release, the most expensive).

SQA is a planned set of activities to ensure software meets quality standards: setting standards, reviews and audits, testing, error collection and analysis, change management and education. A formal technical review (FTR) is a meeting of 3–5 people who examine a work product (design or code) to find errors early. Guidelines: review the product, not the producer; set an agenda; limit debate; keep it under two hours; record issues. Statistical SQA collects defect data, traces each defect to its cause and uses the Pareto principle (80% of defects come from 20% of causes) to fix the vital few causes first. Six Sigma aims for 3.4 defects per million opportunities (DMAIC: Define, Measure, Analyse, Improve, Control).

Reliability is the probability of failure-free operation for a specified time in a specified environment.

• Types of maintenance: corrective (fix bugs), adaptive (adapt to new environments), perfective (improve features) and preventive (avoid future problems).
• End of life (EOL): support stops; users must be informed in advance.
• Migration strategies: parallel running, phased migration or direct cutover, with data migration and user training.