Not every application needs to be built in a heavily layered manner. Not every application needs to be overly extensible. Some applications need to be built quickly and simply for the sole purpose of getting them out the door. However, be careful not to build something simple when something flexible should have been built in its place. While you can easily grow an application that was built with growth in mind, extending an application that was built without growth in mind can be difficult, if not near impossible.

Knowing that our application is going to be a large undertaking that should last for some time, we need to design something that can be easily extended as the need arises. For that we will try to design this application with extensibility in mind. The easiest way to do that is to follow the general rule of maintaining "separation of concerns".