Chapter 17. Use Cases

Use cases are a wonderful idea that has been vastly overcomplicated. Over and over again, I have seen teams sitting and spinning in their attempts to write use cases. Typically, such teams thrash on issues of form rather than substance. They argue and debate over preconditions, post-conditions, actors, secondary actors, and a bevy of other things that simply don't matter.

The real trick to use cases is to keep them simple. Don't worry about use case forms; simply write them on blank paper or on a blank page in a simple word processor or on blank index cards. Don't worry about filling in all the details. Details aren't important until much later. Don't worry about capturing all the use cases; that's an impossible task.

The one thing to remember about use cases is: Tomorrow, they are going to change. No matter how diligently you capture them, no matter how fastidiously you record the details, no matter how thoroughly you think them through, no matter how much effort you apply to exploring and analyzing the requirements: Tomorrow, they are going to change.

If something is going to change tomorrow, you don't need to capture its details today. Indeed, you want to postpone the capture of the details until the last possible moment. Think of use cases as just-in-time requirements.