Five Tips for Finding Non-Functional Requirements

Following on from my previous blog on the challenge of capturing non-functional requirements here are five tips for smoothing that process. These have been worked out through some often painful project experiences and, I hope, will avoid you making some of the mistakes I have seen made in the past if these are not considered.

  1. Really, really think about who your stakeholders are. The process of gathering non-functional requirements should begin with creating a list of the different stakeholders (that is, the people who have an interest or concern in the system under development). These are not just the people who will actually be using the system but also the ones who will be operating it, maintaining it, ensuring it is secure and so on). One of the commonest mistakes I observe is that a key stakeholder is forgotten about until the very end of the project (sometimes just before the system is about to go live ) and a critical NFR is not accounted for.
  2. Consider non-functional and functional requirements together. Some NFRs should be associated directly with functional requirements so need to be considered at the same time. For example discussions about response times (the system must provide a new account number in less than two seconds) are clearly related to the (functional) requirement for opening a new account. It is useful therefore to make sure NFRs are considered at the same time as functional requirements are gathered (otherwise you’re just going to go back and ask questions of the same stakeholders again).
  3. Be an “NFR evangelist”. NFRs seem to be one of those project artefacts which no one wants to own. If this is the case on your project then be that person. Read up and understand the importance of NFRs. Create checklists of the kind of NFRs that need to be gathered. Be ready and prepared to present to users and management alike the importance of NFRs. Have a list of anecdotes at the ready that illustrate the importance of NFRs.
  4. Realise once round the block won’t be enough. Despite your best efforts at understanding stakeholders and looking for NFRs at the time you gather functional requirements there will always be some things that are simply not known early on in the project. It’s not always known what external regulations need to be conformed to early on for example or even what detailed availability or performance requirements are needed. I favour a breadth-first approach here. Make sure that early on you at least capture the categories of NFR (performance, security, regulatory etc) together with the key requirements in each category. Later you can capture missing detail.
  5. Be prepared to challenge peoples prejudices and unreasonableness. Believe it or not some people ask for things which aren’t as reasonable as they might be? 24X7 availability, sub-second response times are typical. Whilst it may be possible to build systems that support such NFRs the cost will probably be prohibitive. Be prepared therefore to challenge such requests and offer alternatives, or at least spell out what the costs will be.

Clearly there is more to gathering and analysing NFRs than is stated here however these are some of the considerations you might want to think about and use to start the process if you find yourself on a project where you are the one who is responsible for this.

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