In object-oriented systems, architectural class diagrams are one of six types of structural diagrams that you can use to model the objects that make up the system, to display the relationships between the objects, and to describe what those objects do and the services that they provide. In simpler words, a class diagram resembles a flowchart in which classes are portrayed as boxes, each box having three rectangles inside. The top rectangle contains the name of the class; the middle rectangle contains the class's attributes; the lower rectangle contains the methods, also called operations, of the class.
