Data Flow Diagrams Data Flow Diagrams (DFDs)(DFDs)

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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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