Non-Functional Requirements versus Quality Attributes

I think that quality attributes represent a subset of non functional requirements.

A non functional requirement, as its name implies, adds no specific behavior to the system, but describes characteristics of the system.

The first synonym of non functional requirement I can think of is
constraint. For instance:

1. the project shall be developed in either ASP.NET or PHP

2. the database shall be SQL Server

3. open source products only shall be used for development and run time

4. the system shall be scalable

5. the system shall implement fault tolerant policies

6. the system shall be designed in order to minimize processing and response time

4 to 6 are also quality attributes, but 1 to 3 aren’t – they just state some constraint to take into account for analysis/design, development and/or runtime.