UML 2 Class Diagrams: An Agile Introduction Search UML 2 class diagrams are the mainstay of object-oriented analysis and design. UML 2 class diagrams show the classes of the system, their interrelationships (including inheritance, aggregation, and association), and the operations and attributes of the classes. Class diagrams are used for a wide variety of purposes, including both conceptual/domain modeling and detailed design modeling. Although I prefer to create class diagrams on whiteboards because simple tools are more inclusive most of the diagrams that I'll show in this article are drawn using a software-based drawing tool so you may see the exact notation. In this article I discuss: • Conceptual class diagrams • Design class diagrams • How to create UML class diagrams • Suggested reading 1. Conceptual Class Diagrams Figure 1 depicts a start at a simple UML class diagram for the conceptual model for a university. Classes are depicted as boxes with three sections, the top one indicates the name of the class, the middle one lists the attributes of the class, and the third one lists the methods. By including both an attribute and a method box in the class I'm arguably making design decisions in my model, something I shouldn't be doing if my goal is conceptual modeling. Another approach would be to have two sections, one for the name and one listing responsibilities. This would be closer to a CRC model (so if I wanted to take this sort of approach I'd use CRC cards instead of a UML class diagram). I could also use class boxes that show just the name of the class, enabling me to focus on just the classes and their relationships. However, if that was my goal I'd be more likely to create an ORM diagram instead. In short, I prefer to follow AM's Apply the Right Artifact(s) practice and use each modeling technique for what it's best at. Figure 1. Sketch of a conceptual class diagram. Home Start Here Best Practices Disciplines Artifacts Resources Contact Us #AgileModeling