rInclude relation: An include relation from one use case to another usecase depicts that the interaction sequence of the first use case includesthe interaction sequence of the other use case.ObjectsSystem boundaryCommunication between actorand use caseUse Case23[name] Use CaseBUse CaseA«extend»Use CaseAUse CaseB«include»Relations[name] [name] Actor (person)Actor(alternative notation)[name]Use caseextend include «actor»[name]«system»[Name] Actor (system)Xsopqr
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666Model-Based Requirements DocumentationsRelation between actors and use cases: If communication between ause case and one or more actors takes place during the execution ofthe use case, the communication must be annotated by means of acommunication relation between the respective actors and the usecase. Example of UML Use Case DiagramsFigure 6-4 shows an example of a use case diagram.Figure 6-4 An example using modeling elements of use case diagramsThe model comprises the use cases “download traffic information”,“retrieve current position”, and “input navigate to destination” elements.The relations in figure 6-4that are labeled by numbers are explained infurther detail below:IncludenThe use case “navigate to destination” is related to the use cases“input destination” and “retrieve current position” via an includerelation. The relationship depicts that the interaction steps defined inthe use cases “input destination” and “retrieve current position” arecontained in the use case “navigate to destination”. ExtendoThe extend relation between the use cases “download trafficinformation” and “navigate to destination” defines that theinteraction steps defined in the use case “download trafficinformation” are included in the interaction steps of the use caseXoX
6.3Use Cases67“navigate to destination” if a certain condition, such as “avoidcongestion”, is met. The extension point “avoid congestion” depictsthe step in the use case “navigate to destination” at which theadditional interaction steps are being executed.GeneralizationUML also provides a generalization relation between use cases or actors.In this case, the specializing use cases or actors inherit the properties of thegeneralizing use case or actor (e.g., [Rumbaugh et al. 2005]). For instance,the actors “service mechanic” and “customer service representative” can begeneralized as the actor “employee”. The generalizing actor would carry allaspects that the actors “service mechanic” and “customer service repre-sentative” have in common (e.g., employee ID).6.3.2Use Case SpecificationsUse case diagrams show the system’s relevant functions from a user’s per-spective and specific relationships between the functions of the system orbetween functions of the system and aspects in the system’s context. Withthe exception of a use case’s name and its relationships, use cases diagrams
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