UML basics: The class diagram

Structure diagrams in general

Structure diagrams show the static structure of the system being modeled. focusing on the elements of a system, irrespective of time. Static structure is conveyed by showing the types and their instances in the system. Besides showing system types and their instances, structure diagrams also show at least some of the relationships among and between these elements and potentially even show their internal structure.

Structure diagrams are useful throughout the software lifecycle for a variety of team members. In general, these diagrams allow for design validation and design communication between individuals and teams. For example, business analysts can use class or object diagrams to model a business's current assets and resources, such as account ledgers, products, or geographic hierarchy. Architects can use the component and deployment diagrams to test/verify that their design is sound. Developers can use class diagrams to design and document the system's coded (or soon-to-be-coded) classes.

The class diagram in particular

UML 2 considers structure diagrams as a classification; there is no diagram itself called a "Structure Diagram." However, the class diagram offers a prime example of the structure diagram type, and provides us with an initial set of notation elements that all other structure diagrams use. And because the class diagram is so foundational, the remainder of this article will focus on the class diagram's notation set. By the end of this article you should have an understanding of how to draw a UML 2 class diagram and have a solid footing for understanding other structure diagrams.

Author: Donald Bell