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Using Using Data flow DiagramsData flow Diagrams

Computer System:

1. Input

2. Data Processing

3. Output

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Data Flow DiagramData Flow DiagramCategorized as :Categorized as : Logical DFDLogical DFD

– focuses on the businessfocuses on the business– how the business operateshow the business operates– current systemcurrent system

Physical DFDPhysical DFD– how the system to be implementedhow the system to be implemented– including including

hardwarehardware software software filesfiles

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AdvantagesAdvantages

Freedom from committing too Freedom from committing too early.early.

Understanding of the Understanding of the interrelatednessinterrelatedness

Communicating to users Communicating to users Analysis the necessary data and Analysis the necessary data and

processesprocesses

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Convention SymbolsConvention Symbols

There are four There are four basic symbols:basic symbols:

1.1. EntityEntity2.2. Data flowData flow3.3. ProcessProcess4.4. Data storeData store

D2

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ExampleExample

EntityEntity

Data flowData flow

ProcessProcess

Data storeData store

Student

2.1

CreateStudentRecord

New Student Information

D3 Student Master

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Developing DFDDeveloping DFD

Creating the context Creating the context diagramdiagram

Drawing diagram 0Drawing diagram 0 Creating child diagramsCreating child diagrams

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Context DiagramContext Diagram

0

SystemName

Entity 1

Entity 2

Entity 3Output C

Input A

Input B

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Diagram 0Diagram 0

4

GeneralProcessDDD

3

GeneralProcessCCC

2

GeneralProcessBBB

1

GeneralProcessAAA

D2 Data store 2D1 Data store 1

Input A

Input B

Input BData Flow B

Data Flow D

E1

E2

E3

Data Flow CRecord A Record E

Record A Record E

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Creating Child DiagramCreating Child Diagram

For each process n create diagram nFor each process n create diagram n Number child process with prefix n.Number child process with prefix n.

– Example: n.1, n.2, n.3, n.4 etcExample: n.1, n.2, n.3, n.4 etc Child diagram depicts detailed Child diagram depicts detailed

processesprocesses Includes all the inputs and outputs Includes all the inputs and outputs

of process nof process n

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Diagram 1Diagram 1

Input A Data Flow B

Data Flow C

Record A

1.1

GeneralProcessAAA 1

1.2

GeneralProcessAAA 2

1.4

GeneralProcessAAA 4

1.3

GeneralProcessAAA 3

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Diagram 2Diagram 2

Input BData Flow B

Record E

2.1

GeneralProcessBBB 1

2.2

GeneralProcessBBB 2

2.3

GeneralProcessBBB 3

D3 Data store 3

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Diagram 3Diagram 3

Input BData Flow D

Record A

3.1

GeneralProcessCCC 1

3.2

GeneralProcessCCC 2

3.3

GeneralProcessCCC 1

3.4

GeneralProcessCCC 4

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Diagram 4Diagram 4

Data Flow D

Record E

4.1

GeneralProcessDDD 1

4.1

GeneralProcessDDD 1

4.1

GeneralProcessDDD 1

D4 Data store 4

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Creating Physical DFDCreating Physical DFD

Convert Convert Logical Data Flow nameLogical Data Flow name To Physical Data Flow nameTo Physical Data Flow name

– customer IDcustomer ID bar code bar code– paymentpayment in cash in cash– paymentpayment by credit card number by credit card number– reportreport send by mail send by mail– reportreport send by email send by email

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Partitioning Data Flow Partitioning Data Flow DiagramDiagram

Examining DFD and divided Examining DFD and divided into collections of: into collections of:

manualmanual procedures procedures computercomputer programs programsFor For implementationimplementation purpose purpose