On the true nature of use cases
April 23, 2008
Use cases are primarily used to make software for knowledge workers. Sure, they are abstract enough and flexible enough to describe users’ interactions with a variety of systems. You could – and perhaps people do – write use cases for driving a car. But most of the time when you see a use case, there is software in the offing.
And what exactly do knowledge workers do? That’s easy. They make decisions in the area of their expertise. They are immersed in a situation made intelligible by their experience and training, and apply their knowledge and reason to make decisions which result in actions.
A user sitting in front of a software screen can only select things. (We can take care of edge cases by describing writing text as selecting one text out of all possible texts, and by describing drawing with a paint program as selecting one picture out of all possible pix, etc.)
Each selection represents a decision – check the box, set that radio button, select this item from a combo box – and the little decisions are rolled up into bigger ones: save, start, do.
There is a range of complexity and sophistication of decision making, and a wide range of the type and depth of expertise a user has to bring to the arena. At the low end, there are binary decisions in simple spaces – open a file? ok. At the high end, there are sophisticated tools that can be used to help analyze complex situations using queuing theory, game theory, probablility, simulation, and other formal techniques. More about the nature of decisions in a future rumination.
So what is the true nature of a use case? A use case is a decision context. It describes an expert engaged in a decision scenario. The overall goal of the use case is reached by a series of such decisions. The expert needs to be immersed in the environment where the decision is possible. They have to be provided with the information, the research, on which to base their decision. And they need to be presented clear and correct selections that correspond to qualifying and making the decision.
As always, more to come.
