Trying to understand the standards (ISO) but so far, I find it very confusing.
50% of books state Functionality naturally belongs under Functional requirements, while the other 50% state that Functionality, as a quality factor, deals with non-funtional aspects of functionality. Some just show a list of NFRs and include Functionality (ISO9127) or Functional suitability (ISO25010), some exclude them explicitly.
What is correct? If these quality models are to present quality factors, those should be truly non-functional but it contradicts the definitions in ISO itself (Degree to which a product or system provides functions that meet stated and implied needs when used under specified conditions = isnt clearly functional?)
An example from Google Books - I really do not understand:
Full model of software quality consists of following non-functional qualities:
-Functional suitability: Degree to which a product or system provides functions that meet stated and implied needs (functional requirements).
So what does the above definiton say? That non-functional characteristic is actually functional?
But in most sources, Functional suitability is considered NFR..one of the many is shown below:
Others say that ISO25010 do not address functional requirements at all...
EDIT: So I believe those claiming that this standard deals with functionality are truly wrong, in the ISO document, I found the following:
The scope of the models excludes purely functional properties (see C.6), but it does include functional suitability (see 4.2.1).