Throughout this book, we focused on building a business application, which in essence makes sure we don't over or under book our dungeon, and more specifically to manage the transfer of prisoners that need to be moved due to the constraints of the dungeon. We, as developers, had to rely heavily on the domain experts guiding us through the development, as we don't have the necessary knowledge of the business domain, yet. In this kind of scenario, the establishment of a language comes in very handy as it allows us to talk in a precise manner about what the problems are and how we can deal with new rules, from then on.

Previously, we have seen that not all domains lend themselves nicely to such a strategy, and even domains that do may contain parts that are best handled by secondary systems. Especially when starting out with a new project, we cannot be sure if it makes sense to invest in a heavy domain layer or not.