For Agile development teams, there are three key modeling concepts that are critical for successful requirements modeling.
First, create model artifacts “just in time” and make them “just good enough”. Creating model artifacts just in time means not trying to produce detailed models too far in advance of when they are needed or when the decisions about the details cannot yet realistically be made. Making models just good enough means not wasting time building models that are more elaborate than needed for the task at hand. Of course, what is “just good enough” depends on the situation and knowing when your models are good enough is critical. A model that is “a little better than necessary” would be far better than a model that is “not quite good enough”.
Second, create model artifacts in an iterative and incremental manner. This goes hand in hand with creating the models just in time and making them just good enough. Each iteration will add depth and breadth to the models. As the scope of each iteration or release is defined it will become clear which parts of the model should be elaborated for that iteration or release. Rather than trying to build a completely detailed model all in one attempt, a more realistic way to construct a complex model is to use progressive elaboration over a series of iterations.
Third, create and manage model artifacts in a way that anticipates change. White boards, flip charts, and note cards are all useful modeling tools and it would be hard for many of us to imagine working without them. They are easy to use and can help us move modeling efforts forward quickly and without a lot of overhead. Unfortunately, they lack the persistence and maintainability we need for progressive elaboration. We need our models in a modeling tool but how we use the tool can have a big impact on our results. Whatever tool you use, think about how you will change and maintain the model as new information becomes available.
There are lots of little details that go into making good models but for the most part they fall into one of these three categories. Focus on these three concepts and your agile modeling efforts will be headed for success.