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Dfd final

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  • 1. DATA FLOWDIAGRAMS(DFDs)
  • 2. Data Flow Diagrams A graphical tool, useful for communicating withusers, managers, and other personnel. Used to perform structured analysis to determinelogical requirements. Useful for analyzing existing as well as proposedsystems. Focus on the movement of data between externalentities and processes, and between processes anddata stores. A relatively simple technique to learn and use.
  • 3. Why DFD ? Provides an overview of- What data a system processes What transformations are performed What data are stored What results are produced and where they flow Graphical nature makes it a good communication toolbetween- User and analyst Analyst and System designer
  • 4. DFD elementsSource/Sinks (External entities)Data flowsProcessesData Stores
  • 5. External Entities A Rectangle representsan external entity They either supply orreceive data They do not process dataExternalEntities• Source – Entity thatsupplies data to thesystem.• Sink – Entity thatreceives data from thesystem.
  • 6. Data Flows Data in motion Marks movement of datathrough the system - a pipelineto carry data. Connects the processes, externalentities and data stores. Generally unidirectional, If samedata flows in both directions,double-headed arrow can beused.Data Flow
  • 7. Processes A circle represents a process Straight line with incoming arrows are input dataflows Straight lines with outgoing arrows are output dataflows Labels are assigned to Data flow. These aiddocumentation1.STORESStores demandnoteDelivery SlipIssue Slip
  • 8. Data Stores A Data Store is a repository of data Data can be written into the data store. This isdepicted by an incoming arrow Data can be read from a data store. This is depictedby an outgoing arrow External entity cannot read or write to the data store Two data stores cannot be connected by a data flowData StoresD1 Data StoresD1 Data StoresD1Writing Reading
  • 9. Rules of Data Flow Data can flow from External entity to process Process to external entity Process to store and back Process to process Data cannot flow from External entity toexternal entity External entity to store Store to external entity Store to store
  • 10. Data Flow DiagramsAn alternate notation is often used: A Process A Data Store3StoreIssueData StoresD1LabelNameNameLabel
  • 11. Good Style in Drawing DFD Use meaningful names for data flows, processes anddata stores. Use top down development starting from contextdiagram and successively levelling DFD Only previously stored data can be read A process can only transfer input to output. It cannotcreate new data Data stores cannot create new data
  • 12. Decomposition of DFDs A system is too complex to be shown on a single DFD. Decomposition is the iterative process of explodingdata flow diagrams to create more detail. Level 0 data flow diagrams may be exploded intosuccessive low levels of detail. The next level of detailwould be a level 1 data flow diagram. The DFDs become linked together ina hierarchy, which would fullydocument the system.
  • 13. Why Level DFD If a DFD is too detailed it will have too manydata flows and will be large and difficult tounderstand Start from a broad overview. Expand to details –Idea similar to using procedures and linkingthese with a main program Each DFD must deal with one aspect of a bigsystem
  • 14. Levels of DFD Context diagram Level-0 diagram (System diagram) Level-n diagram- Detail of one process from nexthighest level Primitive diagram (Lowest level DFD)
  • 15. Levelling Rules If a process p is expanded, the process at the next levelare labelled as p.1, p.2 etc. All data flow entering or leaving p must also enter orleave it’s expanded version Expanded DFD may have data stores No external entity can appear in expanded DFD Keep the number of processes at each level less than 7
  • 16. Balancing DFDs Information presented at onelevel of a DFD is accuratelyrepresented in the next levelDFD. Ensures that the input andoutput data flows of theparent DFD are maintainedon the child DFD.
  • 17. Creating DFDs Create a preliminary Context Diagram. Identify Use Cases, i.e. the ways in which users mostcommonly use the system. Create DFD fragments for each use case. Create a Level 0 diagram from fragments. Decompose to Level 1,2,… Validate DFDs with users.
  • 18. Creating the Context Diagram Draw one process representingthe entire system (process 0) Find all inputs and outputs thatcome from or go to externalentities; draw as data flows. Draw in external entities as thesource or destination of thedata flows.
  • 19. Creating Level 0 Diagram Combine the set ofDFD fragments intoone diagram. Generally move fromtop to bottom, left toright. Minimize crossed lines.
  • 20. Creating Level 1 Diagram Each use case is turned into its own DFD. Take the steps listed on the use case and depicteach as a process on the level 1 DFD. Inputs and outputs listed on use case become dataflows on DFD. Include sources and destinations of data flows toprocesses and stores within the DFD. May also include external entities for clarity.
  • 21. When to stop decomposingDFDs?Ideally, a DFD has at leastthree levels.When the system becomesprimitive i.e. lowest levelis reached and furtherdecomposition is useless.
  • 22. Validating DFD Check for syntax errors toassure correct DFD structure. Check for semantics errors toassure accuracy of DFDrelative to actual/desiredsystem.
  • 23. UniversityAdmissionSystem0StudentStudent InformationReportStaffAdmission Approvalor RejectionReport RequestContext DiagramDFD for University Admission System
  • 24. PerformIntakeProcedure1StudentStudentInformationReportAdmission Approvalor RejectionReport RequestApprovedApplicationVerifiedApprovedApplicationDataQueryDataRequest for StudentInformation MaintenanceOther Student DataData ItemPromptStaffDataItemsGenerateReports3MaintainStudentInformation2StudentName & IDStudent DataD1PriorApplicationDataLevel 0
  • 25. ReceiveAdmissionApplication1.1StudentStudentInformationApplication Approvalor RejectionVerifyAdmissionApplication1.2ReviewAdmissionApplication1.3Admission ApplicationStudent DataD1VerifiedAdmissionApplicationApplicationRequestApplicationDataStudent Nameand IDPriorApplicationDataApproved ApplicationLevel 1 Process 1, Perform Intake Procedure
  • 26. Add NewStudent2.2Edit ExistingStudent2.3DeleteExistingStudent2.4Student DataD1CancelOperation2.5Approved Application to EditID of Studentto DeleteDetermination toCancel OperationDetermineOperation2.1Approved ApplicationRequest for StudentInformation MaintenanceApproved Applicationto AddVerified ApprovedApplicationVerified ChangedStudent DataVerified ID ofStudent to DeleteLevel 1 Process 2, Maintain StudentInformation
  • 27. Context DiagramDFD for Lemonade Stand0.0LemonadeSystemEMPLOYEECUSTOMERPayPaymentOrderVENDORPaymentPurchase OrderProduction ScheduleReceived GoodsTime WorkedSales ForecastProduct Served
  • 28. Level 02.0ProductionEMPLOYEEProductionSchedule1.0Sale3.0Procure-mentSales ForecastProduct OrderedCUSTOMERPayPaymentCustomer OrderVENDORPaymentPurchase OrderOrderDecisionsReceived GoodsTime WorkedInventoryProduct Served4.0Payroll
  • 29. Level 1, Process 11.3ProduceSalesForecastSales ForecastPayment1.1RecordOrderCustomer OrderORDER1.2ReceivePaymentPAYMENTSevered OrderRequest for ForecastCUSTOMER
  • 30. Level 1, Process 2 and Process 32.1ServeProductProduct OrderORDER2.2ProduceProductINVENTORTYQuantity SeveredProductionScheduleRAWMATERIALS2.3StoreProductQuantity Produced &Location StoredQuantity UsedProduction Data3.1ProducePurchaseOrderOrder DecisionPURCHASEORDER3.2ReceiveItemsReceivedGoodsRAWMATERIALS3.3PayVendorQuantityReceivedQuantity On-HandRECEIVEDITEMSVENDORPayment ApprovalPayment
  • 31. Level 1, Process 4Time Worked4.1RecordTimeWorkedTIME CARDS4.2CalculatePayrollPayroll RequestEMPLOYEE4.3PayEmployeeEmployee IDPAYROLLPAYMENTSPayment ApprovalPaymentUnpaid time cards
  • 32. ProcessDecomposition4.1RecordTimeWorked4.2CalculatePayroll4.3PayEmployee3.1ProducePurchaseOrder3.2ReceiveItems3.3PayVendor2.1ServeProduct2.2ProduceProduct2.3StoreProduct1.1RecordOrder1.2ReceivePayment2.0Production1.0Sale3.0Procure-ment4.0Payroll0.0LemonadeSystemLevel 0 Level 1Context Level
  • 33. Logical and Physical DFD DFDs considered so far are called logical DFDs A physical DFD is similar to a document flow diagram It specifies who does the operations specified by thelogical DFD Physical DFD may depict physical movements of thegoods Physical DFDs can be drawn during fact gatheringphase of a life cycle
  • 34. Physical DFD for Cheque EncashmentCashClerkVerify A/CSignature UpdateBalanceBad ChequeStore chequesCustomer AccountsChequeCheque withToken numberCashierVerify TokenTake SignatureEntry in Day BookCUSTOMERTokenToken
  • 35. Logical DFD for Cheque EncashmentCashRetrieveCustomerRecordChequewith tokenStore chequesCustomer AccountsChequeCheque withTokenEntry in DayBookCUSTOMERToken SlipCheque CheckBalance,Issue tokenStore Tokenno &chequesSearch &match tokenUpdateDaily cashbookToken Slipor Cheque
  • 36. Questions? ? ?
  • 37.  In a DFD external entities are represented by aa. Rectangleb. Ellipsec. Diamond shaped boxd. Circle External Entities may be aa. Source of input data onlyb. Source of input data or destination of resultsc. Destination of results onlyd. Repository of data A data store in a DFD representsa. A sequential fileb. A disk storec. A repository of datad. A random access memory
  • 38.  By an external entity we mean aa. Unit outside the system being designed which can be controlled by an analystb. Unit outside the system whose behaviour is independent of the system beingdesignedc. A unit external to the system being designedd. A unit which is not part of DFD A data flow cana. Only enter a data storeb. Only leave a data storec. Enter or leave a data stored. Either enter or leave a data store but not both A circle in a DFD representsa. A data storeb. A an external entityc. A processd. An input unit
  • 39. Thanks foryourCooperation