We admit it. We've only skimmed the top layer of implementation. The larger topic, in its own right, is the design and implementation of complex systems, and there are entire sections in the technical libraries devoted to this challenge. But hopefully, we've provided some techniques you can use to assist with that effort and, more specifically , techniques that can help you implement the right system to begin with. But since this is not a book on implementing software systems, this is as deep as we need to go on that topic. We'll now move on to the next large problem, system testing .