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DEV475 Mastering Object-Oriented Analysis and Design with UMLExample: Finding Boundary ClassesExample: Finding Boundary Classes• One boundary class per actor/use case pairStudentRegister for CoursesCourse Catalog SystemRegisterForCoursesFormCourseCatalogSystemMastering Object Oriented Analysis and Design with UMLCopyright © 2003 Rational Software, all rights reserved 16The goal of Analysis is to form a good picture of how the system is composed, not todesign every last detail. In other words, identify boundary classes only for phenomenain the system or for things mentioned in the flow of events of the Use-CaseRealization.Consider the source for all external events and make sure there is a way for thesystem to detect these events.One recommendation for the initial identification of boundary classes is oneboundary class per actor/use-case pair. This class can be viewed as havingresponsibility for coordinating the interaction with the actor. This may be refined as amore detailed analysis is performed. This is particularly true for window-based GUIapplications where there is typically one boundary class for each window, or one foreach dialog box.In the above example:• The RegisterForCoursesForm contains a Student's "schedule-in-progress." Itdisplays a list of Course Offerings for the current semester from which theStudent may select courses to be added to his or her Schedule.• The CourseCatalogSystem interfaces with the legacy system that provides theunabridged catalog of all courses offered by the university. This class replaces theCourseCatalog abstraction originally identified in Architectural Analysis.6 - 16
Module 6 - Use-Case AnalysisGuidelines: Boundary ClassGuidelines: Boundary Class• User Interface Classes• Concentrate on what information is presented tothe user• Do NOT concentrate on the UI details• System and Device Interface Classes• Concentrate on what protocols must be defined• Do NOT concentrate on how the protocols willbe implementedConcentrate on the responsibilities, not the details!Mastering Object Oriented Analysis and Design with UMLCopyright © 2003 Rational Software, all rights reserved 17When identifying and describing analysis classes, be careful not to spend too muchtime on the details. Analysis classes are meant to be a first cut at the abstractions ofthe system. They help to clarify the understanding of the problem to be solved andrepresent an attempt at an idealized solution (Analysis has been called “idealizedDesign”).User Interface Classes: Boundary classes may be used as “holding places” for GUIclasses. The objective is not to do GUI design in this analysis, but to isolate allenvironment-dependent behavior. The expansion, refinement and replacement ofthese boundary classes with actual user-interface classes (probably derived frompurchased UI libraries) is a very important activity of Class Design and will bediscussed in the Class Design module. Sketches or screen captures from a userinterfaceprototype may have been used during the Requirements discipline toillustrate the behavior and appearance of the boundary classes. These may beassociated with a boundary class. However, only model the key abstractions of thesystem; do not model every button, list, and widget in the GUI.System and Device Interface Classes: If the interface to an existing system or deviceis already well-defined, the boundary class responsibilities should be derived directlyfrom the interface definition. If there is a working communication with the externalsystem or device, make note of it for later reference during design.6 - 17
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