You should have a good understanding of the system flow and the rules by which it will interact with users. At this point, you are ready to create the paper prototype. The paper prototype, also know as the storyboard, is a set of drawings that shows every screen in the system. The objective is to bring the use cases to life and to prove that your system will work when built. The first technical model that we create is the database model.
Database models are perhaps the best understood of all system models.
In nearly all projects, even poorly designed ones, some kind of database model will be created. Most developers are at least familiar with the process of identifying entities and relationships. Although most developers can create a database model, few have actually created a logical model. A logical model represents the software classes in the system. Almost anyone can learn to successfully create use cases, but jumping from use cases to a logical model takes a tremendous amount of experience.