... An Introduction to the Unified Modeling Language Figure 1: The UML symbol for a use case An actor represents whoever or whatever (person, machine, or other) interacts with the system The actor ... information, including the class names, the methods and attributes of the classes, and the relationships among classes © Laurie Williams 2004 An Introduction to the Unified Modeling Language The class diagram ... messages to each other © Laurie Williams 2004 12 An Introduction to the Unified Modeling Language In a sequence diagram, objects are shown in columns, with their object symbol on the top of the line...