Sequence Diagram for the ESU Course Registration System

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Continuing with our analysis of the Add a Course Offering scenario, the diagram is shown in Figure 5-12.

Figure 5-12. Sequence Diagram for the Add a Course Offering Scenario

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Class diagrams may also be attached to use case realizations. These diagrams contain a view of the classes participating in the use case.

CREATING A VIEW OF PARTICIPATING CLASSES IN RATIONAL ROSE

Right-click on the use case realization in the browser to make the shortcut menu visible.
Select the New:Class Diagram menu choice.
While the diagram is still selected, enter the name of the class diagram.
Double-click on the diagram in the browser to open the diagram.
Click to select a class in the logical view of the browser and drag the class onto the diagram.
Repeat step 5 for each additional class that is to be placed onto the diagram.

The View of Participating Classes for the Select Courses to Teach use case is shown in Figure 5-13.

Figure 5-13. View of Participating Classes

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Summary

The use case diagram presents an outside view of the system. The functionality of the use case is captured in the flow of events. Scenarios are used to describe how use cases are realized as interactions among societies of objects. A scenario is an instance of a use case ” it is one path through the flow of events for the use case. Thus, each use case is a web of scenarios. Scenarios are developed to help identify the objects, the classes, and the object interactions needed to carry out a piece of the functionality specified by the use case.

The flow of events for a use case typically is captured in text, whereas scenarios are captured in interaction diagrams. There are two types of interaction diagrams ”sequence diagrams and collaboration diagrams. Each diagram is a graphical view of the scenario.

A sequence diagram shows object interactions arranged in time sequence. A collaboration diagram is an alternate way to show a scenario. This type of diagram shows object interactions organized around the objects and their links to each other.

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Chapter 6. Specifying Relationships

The Need for Relationships
Association Relationships
Aggregation Relationships
Association or Aggregation?
Naming Relationships
Role Names
Multiplicity Indicators
Reflexive Relationships
Finding Relationships
Package Relationships
Summary

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The Need for Relationships

All systems are made up of many classes and objects. System behavior is achieved through the collaborations of the objects in the system. For example, a student is added to a course offering when the course offering receives the add student message. This is often referred to as an object sending a message to another object. Relationships provide the conduit for object interaction. Two types of relationships discovered during analysis are associations and aggregations.

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Association Relationships

An association is a bidirectional semantic connection between classes. It is not a data flow as defined in structured analysis and designdata may flow in either direction across the association. An association between classes means that there is a link between objects in the associated classes. For example, an association between the Course class and the ProfessorCourseManager class means that objects in the Course class are connected to objects in the ProfessorCourseManager class. The number of objects connected depends upon the multiplicity of the association, which is discussed later in this chapter. In the UML, association relationships are shown as a line connecting the associated classes, as shown in Figure 6-1.

CREATING AN ASSOCIATION RELATIONSHIP IN RATIONAL ROSE

Click to select the Association icon from the toolbar. The association icon may be added to the toolbar by right-clicking on the toolbar and selecting the Customize menu command.
Click on one of the associated classes in a class diagram.
Drag the association line to the other associated class.

Figure 6-1. UML Notation for an Association Relationship

An association relationship is shown in Figure 6-2.

Figure 6-2. Association Relationship

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