Software Quality Characteristics (ISO 25010)

About this topic

Source: ISO/IEC 25010:2011 product quality model

Non-functional testing needs a shared vocabulary for what 'good' means, and ISO/IEC 25010 supplies it. These characteristics define the qualities a product can be evaluated against, and Foundation Level draws on them when defining non-functional test types.

The 2011 model organises product quality into eight characteristics, each with sub-characteristics. Functional suitability covers functional completeness, correctness, and appropriateness — whether the functions are all there, whether they produce right results, and whether they suit the task. Performance efficiency covers time behaviour, resource utilisation, and capacity.

Compatibility covers co-existence (running alongside other software without adverse effect) and interoperability (exchanging and using information with other systems). Usability covers appropriateness recognizability, learnability, operability, user error protection, user interface aesthetics, and accessibility. Reliability covers maturity, availability, fault tolerance, and recoverability — a system that fails but recovers cleanly is more reliable than one that fails rarely but catastrophically.

Security covers confidentiality, integrity, non-repudiation, accountability, and authenticity. It is a product quality characteristic in its own right, not a subdivision of reliability, which is a distinction the exam can test directly.

Maintainability covers modularity, reusability, analysability, modifiability, and testability. Testability appears here as a property of the product, which is worth noting: how easily a system can be tested is a design outcome, not a testing decision. Portability covers adaptability, installability, and replaceability.

A note on editions: the content above is ISO/IEC 25010:2011, which is the edition the ISTQB CTFL syllabus references and therefore the one to learn for the exam. The 2023 revision renamed Usability to Interaction Capability and Portability to Flexibility, added Safety as a ninth characteristic, and moved quality-in-use into ISO/IEC 25019. Expect the 2011 names in exam questions.

Distinct from the characteristics themselves are the philosophical views of what quality means — transcendent, product-based, user-based, manufacturing-based, and value-based. These framings sit behind any discussion of quality and explain why stakeholders disagree even when they agree on the measurements, but they are not enumerated or examined at Foundation Level.

What this topic covers

• Functional suitability
• Performance efficiency
• Compatibility and interoperability
• Usability
• Reliability and recoverability
• Security
• Maintainability and testability
• Portability