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DREXEL CS 451 - modeling

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©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 7 Slide 1System modelsz Abstract descriptions of systems whose requirements are being analysed©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 7 Slide 2System modellingz System modelling helps the analyst to understand the functionality of the system and models are used to communicate with customersz Different models present the system from different perspectives– External perspective showing the system’s context or environment– Behavioural perspective showing the behaviour of the system– Structural perspective showing the system or data architecture©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 7 Slide 3Structured methodsz Structured methods incorporate system modelling as an inherent part of the methodz Methods define a set of models, a process for deriving these models and rules and guidelines that should apply to the modelsz CASE tools support system modelling as part of a structured method©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 7 Slide 4Method weaknessesz They do not model non-functional system requirementsz They do not usually include information about whether a method is appropriate for a given problemz They may produce too much documentationz The system models are sometimes too detailed and difficult for users to understand©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 7 Slide 5Model typesz Data processing model showing how the data is processed at different stagesz Composition model showing how entities are composed of other entitiesz Architectural model showing principal sub-systemsz Classification model showing how entities have common characteristicsz Stimulus/response model showing the system’s reaction to events©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 7 Slide 6Context modelsz Context models are used to illustrate the boundaries of a systemz Social and organisational concerns may affect the decision on where to position system boundariesz Architectural models show the a system and its relationship with other systems©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 7 Slide 7The context of an ATM systemAuto-tellersystemSecuritysystemMaintenancesystemAccountdatabaseUsagedatabaseBranchaccountingsystemBranchcountersystem©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 7 Slide 8Process modelsz Process models show the overall process and the processes that are supported by the systemz Data flow models may be used to show the processes and the flow of information from one process to another©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 7 Slide 9Equipment procurement processGet costestimatesAcceptdelivery ofequipmentCheckdelivereditemsValidatespecificationSpecifyequipmentrequiredChoosesupplierPlaceequipmentorderInstallequipmentFindsuppliersSupplierdatabaseAcceptdeliveredequipmentEquipmentdatabaseEquipmentspec.Checkedspec.DeliverynoteDeliverynoteOrdernotificationInstallationinstructionsInstallationacceptanceEquipmentdetailsChecked andsigned order formOrderdetails +Blank orderformSpec. +supplier +estimateSupplier listEquipmentspec.©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 7 Slide 10Behavioural modelsz Behavioural models are used to describe the overall behaviour of a systemz Two types of behavioural model are shown here– Data processing models that show how data is processed as it moves through the system– State machine models that show the systems response to eventsz Both of these models are required for a description of the system’s behaviour©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 7 Slide 11Data-processing modelsz Data flow diagrams are used to model the system’s data processingz These show the processing steps as data flows through a systemz Intrinsic part of many analysis methodsz Simple and intuitive notation that customers can understandz Show end-to-end processing of data©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 7 Slide 12Order processing DFDCompleteorder formOrderdetails +blankorder formValidateorderRecordorderSend tosupplierAdjustavailablebudgetBudgetfileOrdersfileCompletedorder formSignedorder formSignedorder formChecked andsigned order+ ordernotificationOrderamount+ accountdetailsSignedorder formOrderdetails©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 7 Slide 13Data flow diagramsz DFDs model the system from a functional perspectivez Tracking and documenting how the data associated with a process is helpful to develop an overall understanding of the systemz Data flow diagrams may also be used in showing the data exchange between a system and other systems in its environment©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 7 Slide 14CASE toolset DFDDesigneditorDesigncross checkerDesignanalyserReportgeneratorDesigndatabaseCode skeletongeneratorDesigndatabaseInputdesignValiddesignCheckeddesignDesignanalysisUserreportandReferenceddesignsCheckeddesignOutputcode©Ian Sommerville 1995/2000 (Modified by Spiros Mancoridis 1999) Software Engineering, 6th edition. Chapter 7 Slide 15State machine modelsz These model the behaviour of the system in response to external and internal eventsz They show the system’s responses to stimuli so are often used for modelling real-time systemsz State machine models show system states as nodes and events as arcs between these nodes. When an event occurs, the system moves from one


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