Is There a Common Functionality?

Every systems engineer is familiar with the distinction between what a system is, i.e. its composition in terms of physical components hardware and software, and what a system does, i.e. its functionality. And many of us also commonly work with functionality in the sense that we use the system concept to decompose a complex functionality into a set of interacting functional elements, thereby creating a system in the functional domain, the latter being the set of all functional elements. But whereas we all understand physical components very well how to categorise them, measure them, visualise them, interconnect them, and so on it is not clear that we can say the same for our understanding of functional elements.