Now that our development environment is in place, let's put together a domain model for our problem. A domain model describes the important concepts in the problem domain in a way that can be implemented in software. There are different techniques of preparing a domain model and there are different ways of representing a domain model. The most commonly used representation of a domain model is a class diagram. We will prepare a class diagram and define our classes and their attributes and relations on the basis of the knowledge that we have so far about our problem. I am going to take a slightly agile approach at this. What I mean by this is that I am not going to overly analyze anything here. We will prepare a very simple domain model that covers most of my requirements to a certain degree of comfort. As I go on implementing the features, I will uncover a lot of hidden domain knowledge, which will help me shape my domain model better.