It's 4th of Jan 2016 and let me wish you a happy new year before I get into the subject.
NFRs (Non-functional requirements) are poor cousins of functional requirements (FRs). Tomes have been written about functional requirements, how to express them in text form, how to model them (UML and what not). NFRs hardly find much mention, forget about their modeling.
Many requirements analysts almost deal non-functional requirements as non-critical requirements.
However, if one looks carefully, NFRs actually matter much more than FRs. I usually draw a parallel between building construction and software construction.
When we construct a building, there are architectural aspects and then there are functional aspects. Aspects like building foundation can not be changed and hence need careful attention. Whereas aspects such as interior design, color, placement of lights etc. can be changed without much difficulty and at much lower cost.
Are there requirements which are extremely hard to change? Can you make a product support multiple languages if it is not architected properly? Most likely no.
Are there aspects which are easy to change? A little extra functionality can always be built by spending a developer-month effort.
In my opinion, what one needs to worry in the beginning are those requirements which are hard to change. In fact, majority of the NFRs tend to affect architecture, hence need to be established prior to diving down functional requirements.
Then why is it so that we delve into FRs in the beginning than NFRs? Primarily because it is easy to establish FRs than NFRs. Users are more comfortable with FRs than NFRs. But let us remember, because something is more difficult to establish, does not mean it is less important.
It is my humble request to all fellow requirements analysts and business analysts, do spend a good time on NFRs- it will keep your application much more useful to stakeholders over a longer period of time.
In case you would like to explore NFRs in detail, do take a look at our video https://www.youtube.com/watch?v=Cm29ac1d2as
Happy reading and have a wonderful day and do provide your suggestions and comments.