Functionality in ISO 9126 is Non-functional quality? Contradiction in ISTQB and many sources

by John V   Last Updated May 15, 2019 19:05 PM

I have been doing some research and realized that I missed the fact that in ISO 9126 and ISO 25010, all characteristics are quality characteristics and represent (according to various papers) just non-functional ones. It surprised me as I thought "Functionality" is clearly functional but now I can see that they probably mean "evaluation of functionality from the non-functional view, i.e. how is the system doing these things".

Then I found an interesting thing in an ISTQB book. They talk about functional tests and reference ISO 9126 Functionality. But in the non-functional testing section, they enumerate non-functional requirements according to this ISO and do state Functionality, referencing the section in Functional testing page!

ISO 25010 is said to present 8 non-functional categories, including Functional suitability. That does sound like a non functional one but again it is said it is just renamed Functionality from ISO 9126. And yet there are books saying that "Functional suitability" from ISO 25010 is functional and should be tested functionally (well, it does make sense more than saying it is non-functional)...

Most of the QA books typically lists ISO 9126 Functionality under Functional testing so I cannot understand how this can be listed as non-functional...

Similarly, I found for the ISO 9126 sources claiming that its Functionality is quality requirement, therefore non-functional requirement, while the other sources state that non-functional are those except for this one.

Does anyone know this ISO standard well enough to explain the problem?

Answers 2

Look at the quality model listed here. Every one of those qualities is non-functional.

Functionality that fulfills the business's needs is determined by your functional software requirements. Each functional requirement should be accompanied by an acceptance test, and it is that acceptance test (and not some ISO standards document) that dictates whether or not that functional requirements is fulfilled.

Hypothetically, an ISO document might address the way the requirement and its acceptance test are written and executed, but not the nature of the functional requirements themselves. Functional requirements are wholly dependent on the needs of the stakeholders.

Robert Harvey
Robert Harvey
June 10, 2015 14:19 PM

Software Quality(A general description) measures whether the software satisfies its requirements. Software requirements are classified as either

Non-functional requirement(quality attribute) or Functional requirement

ISo 9126 model is an international standard for evaluation of software quality. <>

May 15, 2019 17:35 PM

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