The use case definition in UML

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Goals wocould be the greatest interest. 3. use caes and ad value: the Key attings in use case work is focus on the question: How can we use the system provide the observable (refer: obeserve patern) value to the user, or fulfil their goals, but not feature list. 4. use Case and functianl requirements: Use case is a requirement that define a promise or contract of how a System wil behave, so it is not the order-style, and a list of system functional requirement. 5.use case is comonly the blackbox, it define the system responsibility, so it is to specify what the system must to do (the functional requirment) without deciding howhowhowhow it wil do it (design ). this point is useful to grap the intent of actors goals also. 6. notes of Use Case sections :. 1 preconditions: it is always true, it is a condition implies a scenario of another use case but it shoshould not of practical value to write.2. postcondition: shocould met the neds of Al stakeholders.3. main scenario: it is basic flow, so no any condition or branching. there are thre kinds ,. A an interaction betwen actors. B A validation from system C. A state change by the system (recording or modifying) the steps in main scenario is indicate the triger event that start the scenaria but not the clasification.4.extensions: An externsion has two part: codition (something that can be detected by the system or an actor) and handling: 5. * A, means at any time. 7. goals and scope of a use case: Use Case Has diferent level as already memtions,