Application structure: Concepts & Features

I spoke about this topic quite a bit in ALT.Net Seattle. This is mostly relating to application architecture and how you structure your application. This is the logical result of applying the Open Closed and Single Responsibility Principles. Feature may not be as overloaded a term in our industry as a service, but it still important to define exactly what I mean. A feature, in my eyes, is a discrete part of the application that perform some operation. That is pretty vague, I know, but I hope that the examples I am going to go through later would make it clearer. So far, it is pretty much the standard fare, but I have a few rules about a feature, the most important of them is: