What Is a Model?
A model is an abstraction of something that lets you thoroughly understand it. A model provides a roadmap for a database, similar to a blueprint for a building that is studied and revised many times before it is built. Models reduce the difficulty of developing software because they let you separate deep conceptual issues from distracting and relatively straightforward implementation details. Models have several specific qualities:
Abstraction. A model suppresses detail and focuses on the essence of a problem.
Basis in reality. A model helps you organize software in correspondence to the real world.
Simplification. You can focus on particular aspects of an application instead of having to deal with the entire application at once.
Abridgement. Because it abstracts and simplifies an application, a model also reduces the size of a problem.