DEV475 Mastering Object-Oriented Analysis and Design with UML ...

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DEV475 Mastering Object-Oriented Analysis and Design with UMLWhat Is a Boundary Class?What Is a Boundary Class?• Intermediates between the interface andsomething outside the system• Several Types• User interface classes• System interface classes• Device interface classes• One boundary class per actor/use-case pairAnalysis classstereotypeMastering Object Oriented Analysis and Design with UMLCopyright © 2003 Rational Software, all rights reserved 14Environment DependentA boundary class intermediates between the interface and something outside thesystem. Boundary classes insulate the system from changes in the surroundings (forexample, changes in interfaces to other systems and changes in user requirements),keeping these changes from affecting the rest of the system.A system can have several types of boundary classes:• User interface classes—Classes that intermediate communication with humanusers of the system.• System interface classes—Classes that intermediate communication with othersystems. A boundary class that communicates with an external system isresponsible for managing the dialog with the external system; it provides theinterface to that system for the system being built.• Device interface classes—Classes that provide the interface to devices whichdetect external events. These boundary classes capture the responsibilities of thedevice or sensor.One recommendation for the initial identification of boundary classes is oneboundary class per actor/use-case pair.6 - 14
Module 6 - Use-Case AnalysisThe Role of a Boundary ClassThe Role of a Boundary ClassActor 1Actor 2Model interaction between the system and its environmentMastering Object Oriented Analysis and Design with UMLCopyright © 2003 Rational Software, all rights reserved 15A boundary class is used to model interaction between the system's surroundings andits inner workings. Such interaction involves transforming and translating events andnoting changes in the system presentation (such as the interface).Boundary classes model the parts of the system that depend on its surroundings. Theymake it easier to understand the system because they clarify the system's boundariesand aid design by providing a good point of departure for identifying related services.For example, if you identify a printer interface early in the design, you will realize thatyou must also model the formatting of printouts.Because boundary classes are used between actors and the working of the internalsystem (actors can only communicate with boundary classes), they insulate externalforces from internal mechanisms and vice versa. Thus, changing the GUI orcommunication protocol should mean changing only the boundary classes, not theentity and control classes.A boundary object (an instance of a boundary class) can outlive a use-case instance if,for example, it must appear on a screen between the performance of two use cases.Normally, however, boundary objects live only as long as the use-case instance.6 - 15
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