Use-case driven software development processes can seriously compromise the ability of systems to evolve if a careful distinction is not made between “structure” and “use”, and this distinction is not reflected immediately in the first model and carried through to the implementation. By “structure”, we are referring to what derives from the nature of the application domain, i.e. to what are perceived to be the “ invariants” or core concepts of the business domain, as opposed to the business rules that apply at a given moment and determine the way the system (solution) will be used.