ABSTRACT
So far in this learning iteration, I have focused on principles and concepts of compositional design. In this chapter I will return to the pay station case and the practical aspects. The learning focus is variability along several dimensions, i.e. when our production code must support combinations of variable aspects. Even in simple systems, you often see this kind of combined variability: a system must interface different types of hardware, run both in a production and test environment, use different types of persistent storage, handle different customer requirements, etc.
