A class diagram is a type of diagram used in software engineering to give an overview of a software system by displaying classes, attributes, operations, and their relationships between each other. It is a static diagram that represents the static view of an application. A class in a UML diagram is a blueprint used to create an object or set of objects, and it defines what an object can do. In a class diagram, a class is depicted as a rectangle with three sections: the top section contains the class name, the middle section contains the instance variables (attributes), and the bottom section contains the methods (behaviors) . The two major types of relationships between classes are association and inheritance. Class diagrams are widely used in the modeling of object-oriented systems because they are the only UML diagrams that can be mapped directly with object-oriented languages. They are used to describe the static view of the system, show the collaboration among the elements of the static view, describe the functionalities performed by the system, and construct software applications using object-oriented languages.