Learning UML

Sequence Diagrams

A sequence diagram shows elements as they interact over time, showing an interaction or interaction instance. Sequence diagrams are organized along two axes: the horizontal axis shows the elements that are involved in the interaction, and the vertical axis represents time proceeding down the page. The elements on the horizontal axis may appear in any order.

Elements

Sequence diagrams are made up of a number of elements, including class roles, specific objects, lifelines, and activations. All of these are described in the following subsections.

Class roles

In a sequence diagram, a class role is shown using the notation for a class as defined in Chapter 3, but the class name is preceded by a forward slash followed by the name of the role that objects must conform to in order to participate within the role, followed by a colon. Other classes may also be shown as necessary, using the notation for classes as defined in Chapter 3.

Class roles and other classes are used for specification-level collaborations communicated using sequence diagrams. Figure 6-8 shows the projectOrganization class role as well as the Project and Report classes.

Figure 6-8. A class role and two classes

Specific objects

In a sequence diagram, a specific object of a class conforming to a class role is shown using the notation for objects as defined in Chapter 3, but the object name is followed by a forward ...