I'm trying to understand the difference between non-functional requirements and quality attributes. Are they the same thing?
You can find a set of quality attributes in the ISO 9126, now ISO/IEC 2500xx SQuaRE family of standards.
I know that each system is defined by a set of functional requirements and every of this requirements has associated one or more quality attributes. For example, suppose that you have the requirement that describes the login functionality of a system. You can associate to that requirement the attributes of security and performance.
If I say that the system can not take more than 1 second to respond, I'm talking about a constraint.
So, where the concept of non-functional requirements kicks in? Are they defined by the users? How can I identify them?