Software quality characteristics
The quality model of ISO/IEC 25010 (2011 version): its eight characteristics and their sub-characteristics, internal and external quality, one measure per characteristic, and the trade-offs between them.
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ISO/IEC 25010: what is it?
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The standard that describes a software product quality model in eight characteristics, each split into sub-characteristics.
The eight characteristics of the 2011 version are functional suitability, performance efficiency, compatibility, usability, reliability, security, maintainability and portability.
A payroll module has no tests and every change breaks something else. Which sub-characteristics are hit hardest?
- Testability and modifiability, of maintainability
- Maturity and fault tolerance, of reliability
- Interoperability and co-existence, of compatibility
- Operability and user error protection, of usability
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Testability and modifiability, of maintainability
The cost and risk of a change belong to maintainability. Reliability describes behaviour at run time, not how easy the code is to modify.
In ISO/IEC 25010, a … is split into …: testability, for example, belongs to maintainability.
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In ISO/IEC 25010, a characteristic is split into sub-characteristics: testability, for example, belongs to maintainability.
A characteristic is assessed through its sub-characteristics, each easier to measure.
Software quality: what is it?
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The degree to which software satisfies stated and implied needs under given conditions of use.
It is not just the absence of bugs: software with no defect that is slow, unreadable or impossible to evolve is poor quality.
A company requires a 16-character password changed every month. Employees stick it on their screen. Which characteristic was sacrificed, and for what?
- Performance was sacrificed to reliability
- Portability was sacrificed to maintainability
- Nothing was sacrificed: a stricter rule always strengthens security
- Usability was sacrificed to security, which ends up weaker
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Usability was sacrificed to security, which ends up weaker
Characteristics can pull against each other: a rule too heavy for the user pushes them to get around it, and real security drops. Trade-offs must follow actual use rather than piling up requirements.