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

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DEV475 Mastering Object-Oriented Analysis and Design with UMLWhat Is a Control Class?What Is a Control Class?• Use-case behavior coordinator• More complex use cases generally require oneor more control casesUse CaseAnalysis classstereotypeUse-case dependent, Environment independentMastering Object Oriented Analysis and Design with UMLCopyright © 2003 Rational Software, all rights reserved 22Control classes provide coordinating behavior in the system. The system can performsome use cases without control classes by using just entity and boundary classes. Thisis particularly true for use cases that involve only the simple manipulation of storedinformation. More complex use cases generally require one or more control classesto coordinate the behavior of other objects in the system. Examples of control classesinclude transaction managers, resource coordinators, and error handlers.Control classes effectively decouple boundary and entity objects from one another,making the system more tolerant of changes in the system boundary. They alsodecouple the use-case specific behavior from the entity objects, making them morereusable across use cases and systems.Control classes provide behavior that:• Is surroundings-independent (does not change when the surroundings change).• Defines control logic (order between events) and transactions within a use case.• Changes little if the internal structure or behavior of the entity classes changes.• Uses or sets the contents of several entity classes, and therefore needs tocoordinate the behavior of these entity classes.• Is not performed in the same way every time it is activated (flow of eventsfeatures several states).Although complex use cases may need more than one control class it isrecommended, for the initial identification of control classes, that only one controlclass be created per use case.6 - 22
Module 6 - Use-Case AnalysisThe Role of a Control ClassThe Role of a Control ClassActor 1Actor 2Coordinate the use-case behaviorMastering Object Oriented Analysis and Design with UMLCopyright © 2003 Rational Software, all rights reserved 23A control class is a class used to model control behavior specific to one or more usecases. Control objects (instances of control classes) often control other objects, sotheir behavior is of the coordinating type. Control classes encapsulate use-casespecificbehavior.The behavior of a control object is closely related to the realization of a specific usecase. In many scenarios, you might even say that the control objects "run" the Use-Case Realizations. However, some control objects can participate in more than oneUse-Case Realization if the use-case tasks are strongly related. Furthermore, severalcontrol objects of different control classes can participate in one use case. Not all usecases require a control object. For example, if the flow of events in a use case isrelated to one entity object, a boundary object may realize the use case incooperation with the entity object. You can start by identifying one control class perUse-Case Realization, and then refine this as more Use-Case Realizations areidentified, and commonality is discovered.Control classes can contribute to understanding the system, because they representthe dynamics of the system, handling the main tasks and control flows.When the system performs the use case, a control object is created. Control objectsusually die when their corresponding use case has been performed.6 - 23
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