C H A P T E R  4

Requirements

The hardest single part of building a software system is deciding what to build. No other part of the conceptual work is as difficult in establishing the detailed technical requirements, including the interfaces to people, to machines, and to other software systems. No other part of the work so cripples the results if done wrong. No other part is more difficult to rectify later. Therefore, the most important function that the software builder performs for the client is the iterative extraction and refinement of the product requirements.

—Fred Brooks¹

Before you start coding – yes, before you start coding – you need to know what it is you're going to build. That's what requirements are: a list of stuff you have to implement in order to create your terrific program. Most developers hate requirements. Really, all we'd like to do is sit down and start coding. All of us have that super-programmer mentality; just give me the problem and I can sit down and design and code it on the fly. Not! If you want to be a productive developer and make fewer errors and come up with a good, clean design, you need requirements – the more detailed the better. A good set of requirements tells you just what the program is supposed to do. It gives you the scaffolding around which you'll hang your design. You'll do requirements anyway – it's one o....