What're the differences between this angle and the traditional one? The biggest difference is that, in the traditional view, the design process and the coding process are two disjointed steps. This separation cuts off the design activity from the coding activity. That is, you only do design in the design stage and you only write code in the implementation stage. This is, in fact, a failure to recognize that, when writing code inside our brain, what's happening is not a simple translation from the design to the source code, but an intense creative activity carried out by the brain.

On the other hand, when we say the source code is the design, it doesn't mean we are against using UML diagrams or any other tools and notations. In fact, we should use anything that helps to create the design. It's just that we must keep in mind that the source code is the final design and the other design documents are auxiliary documentation, which is as important for a software project as design blueprints are for building a house.

In this book, we consider that the source code is the design. And before we talk about how to do code design in Agile projects, let's look at different levels of code design.