The second thing which is relevant to use cases are the actors. We can say that use cases are nothing but the system functionalities written in an organized manner.

When the requirements of a system are analyzed, the functionalities are captured in use cases. Use case diagrams are considered for high level requirement analysis of a system. Show the interaction among the requirements are actors. Identify the external and internal factors influencing the system.

Used to gather the requirements of a system. In brief, the purposes of use case diagrams can be said to be as follows − When the initial task is complete, use case diagrams are modelled to present the outside view. Hence, when a system is analyzed to gather its functionalities, use cases are prepared and actors are identified. These requirements are mostly design requirements. Use case diagrams are used to gather the requirements of a system including internal andĮxternal influences. We will look into some specific purpose, which will distinguish it from other four diagrams. However, this definition is too generic to describe the purpose, as other four diagrams (activity, sequence, collaboration, and Statechart) also have the same purpose. The purpose of use case diagram is to capture the dynamic aspect of a system. Hence to model the entire system, a number of use case diagrams are used. A single use case diagram captures a particular functionality of a system. The diagram is used to model the system/subsystem of an application. Use case diagrams consists of actors, use cases and their relationships. These internal and external agents are known as actors. Now as we have to discuss that the use case diagram is dynamic in nature, there should be some internal or external factors for making the interaction. In UML, there are five diagrams available to model the dynamic nature and use case diagram is one of them. Only static behavior is not sufficient to model a system rather dynamic behavior is more important than static behavior. Dynamic behavior means the behavior of the system when it is running/operating. To model a system, the most important aspect is to capture the dynamic behavior.

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