Use cases look at the requirements from the standpoint of an end user working with the program and how the program responds to the user’s inputs. At its simplest level, a use case can be thought of as a play where the end user is one actor and the program is another actor. These two actors then have dialogs which explain the interactions between the actors. More complicated scenarios can have additional actors including other programs, other types of users, and even hardware. Use cases have proven to be very easy to read and understand even for non-technical clients.
Each use case explores what happens when something goes wrong in addition to the “normal” interactions. The exploration of these failure conditions is very important because these cases are the most difficult to code and can cause the most amount of testing. Traditional requirements often ignore these cases. It can be helpful to have developers and testers both think of additional possible failures in a use case so they can be fully documented in the requirements.
Use cases do not provide a complete picture of the system though. A technical specification should also be included in the requirements to detail formulas and routines that take place behind the scenes.