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Data Flow Diagrams (DFDs). Data Flow Diagrams (DFDs). Data flow diagram (DFD) is a picture of the movement of data between external entities and the processes and data stores within a system. Data-flow models are an intuitive way of showing how data is processed by a system. - PowerPoint PPT Presentation
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Data Flow Diagrams (DFDs)Data Flow Diagrams (DFDs)Data flow diagram (DFD) is a picture of the
movement of data between external entities and the processes and data stores within a system.
Data-flow models are an intuitive way of showing how data is processed by a system.
Data-flow models are used to show how data flows through a sequence of processing steps.
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Data Flow Diagrams (DFDs)Data Flow Diagrams (DFDs)DFDs are particularly useful during the
analysis of requirements as they can be used to show end-to-end processing in a system.
That is, they show the entire sequence of actions that take place from an input being processed to the corresponding output that is the system's response.
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DFD Symbols (Gane & DFD Symbols (Gane & Sarson)Sarson)
Process
Data Flow
Data Store
Source/Sink (External Entity)
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ProcessProcess
Work or actions performed on data (inside the system)
Labels should be verb phrasesReceives input data and produces output
1.0
ProduceGradeReport
Grade Detail Grade Report
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Rule 1: ProcessRule 1: Process
Can have more than one outgoing data flow or more than one incoming data flow
1.0
GradeStudent Work
Student Grade
Submitted WorkGraded Work
3.0
Calculated Gross Pay
Hours Worked
Pay RateGross Pay
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Rule 2: ProcessRule 2: Process
Can connect to any other symbol (including another process symbol)
1.0
VerifyOrder
2.0
Assemble Order
Order Accepted OrderInventory Change
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Data StoreData Store
Is used in a DFD to represent data that the system stores
Labels should be noun phrases
StudentsD1
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Rule: Data StoreRule: Data Store
Must have at least one incoming and one outgoing data flow
Daily Payments
D1
Customer Payment
Daily Payment
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Source/Sink (External Entity)Source/Sink (External Entity)
External entity that is origin or destination of data (outside the system)
Is the singular form of a department, outside organization, or person
Labels should be noun phrases
CUSTOMER
1.0
VerifyOrder
Order
Invoice
Source – Entity that supplies data to the system
Sink – Entity that receives data from the system
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Rule: Source/SinkRule: Source/Sink
Must be connected to a process by a data flow
BANK
2.0
Prepare Deposit
BankDeposit
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The context of an ATM The context of an ATM systemsystem
Auto-tellersystem
Securitysystem
Maintenancesystem
Accountdatabase
Usagedatabase
Branchaccounting
system
Branchcountersystem
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Rules for Using DFD SymbolsRules for Using DFD Symbols
Data Flow That ConnectsYES NO
A process to another process
A process to an external entity
A process to a data store
An external entity to another external entity
An external entity to a data store
A data store to another data store
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Exercise:Precision Tools sells a line of high-quality woodworking tools. When customers place orders on the company’s Web site, the system checks to see if the items are in stock, issues a status message to the customer, and generates a shipping order to the warehouse, which fills the order. When the order is shipped, the customer is billed. The system also produces various reports. Draw a context diagram for the order system Draw DFD diagram for the order system
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Identify Entities,Process,Data Stores & Data FlowIdentify Entities,Process,Data Stores & Data FlowEntities
◦ Customer◦ Warehouse◦ Accounting
Processes◦ 1.0 Check Status ◦ 2.0 Issue Status Messages◦ 3.0 Generate Shipping
Order◦ 4.0 Manage Accounts
Receivable◦ 5.0 Produce Reports
Data Stores◦ D1 Pending Orders◦ D2 Accounts Receivable
Data Flows Order In-Stock Request Order Data Status Data Status Message Shipping Order Order Data Invoice Shipping Confirmation Payment Accounting Data Accounts Receivable Data Order Data Inventory Reports
1.0
2.0
3.0
4.0
5.0
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ACCOUNTING
WAREHOUSECUSTOMER
0
Order System
Order
Payment
In-StockRequest
StatusMessage
Invoice Shipping Confirmation
Shipping Order
Inventory Reports
Context Diagram of Order System
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1.0
CheckStatus
2.0
IssueStatus
Messages
3.0
GenerateShipping
Order
ACCOUNTING
CUSTOMER WAREHOUSE
4.0
Manage Accounts
Receivable5.0
ProduceReports
Order In-Stock Request
Status Data
Status Message
PendingOrdersD1
Order Data
Order Data
Shipping Order
Shipping Confirmation
Invoice
Payment
Accounts ReceivableD2
Accounting Data Accounts Receivable Data
Order Data
Inventory ReportsDFD of
Order System
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