ISBN : 978-81-963532-2-3 (E-Book) casesrepresent the different ways in which a system can be used by the users. A simple way to find allthe use cases of a system is to ask the question: “What the users can do using the system?” ThusfortheLibraryInformation System (LIS), theusecasescould be: • issue-book • query-book • return-book • create-member • add-book,etc Use cases correspond to the high-level functional requirements. The use cases partition thesystem behavior into transactions, such that each transaction performs some useful action fromthe user’s point of view. To complete each transaction may involve either a single message ormultiplemessageexchanges betweentheuser andthe system tocomplete. Purposeofusecases The purpose of a use case is to define a piece of coherent behavior without revealing the internalstructure of the system. The use cases do not mention any specific algorithm to be used or theinternaldatarepresentation,internalstructureofthesoftware,etc.Ausecasetypicallyrepresents a sequence of interactions between the user and the system. These interactions consistof one mainline sequence. The mainline sequence represents the normal interaction between auser and the system. The mainline sequence is the most occurring sequence of interaction. Forexample, the mainline sequence of the withdraw cash use case supported by a bank ATM drawn,complete the transaction, and get the amount. Several variations to the main line sequence mayalsoexist.Typically,avariationfromthemainlinesequenceoccurswhensomespecificconditions hold. For the bank ATM example, variations or alternate scenarios may occur, if thepassword is invalid or the amount to be withdrawn exceeds the amount balance. The variationsare also called alternative paths. A use case can be viewed as a set of related scenarios tiedtogetherbyacommongoal. Themainlinesequenceandeachofthevariationsarecalledscenarios or instances of the use case. Each scenario is a single path of user events and systemactivitythroughthe usecase. Representation of Use Cases Use cases can be represented by drawing a use case diagram and writing an accompanying text 60 Software Engineering Keerthana P, Manasa KN, Ganga D Bengal
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