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Data Flow Diagrams (DFDs)

Data fow diagram (DFD) is a picture o the

movement o data between externalentities and the processes and data stores

within a system



DFD Symbols

Process

Data Flow

Data Store

Source/Sink (External Entity)



Process

Wor or actions perormed on data (inside the

system)

!abels should be verb phrases

"eceives input data and produces output

#ust be numbered



"ule $% Process&an have more than one outgoing data fow or

more than one incoming data fow



"ule '% Process



Process% &orrectncorrect?



Data Flow

s a path or data to move rom one part o the S to

another

*rrows depicting movement o data

&an represent fow between process and data store

by two separate arrows



Data Flow% &orrectncorrect?

+o Data Storeto another

withoutprocess



Data Store

s used in a DFD to represent data that the

system stores

!abels should be noun phrases



"ule% Data Store#ust have at least one incoming and one outgoing data

fow



Data Store% &orrectncorrect?

#usthaveinput



SourceSin (,xternal ,ntity)

,xternal entity that is origin or destination o data-

!ie a department. outside organi/ation. other S.

or person

!abels should be noun phrases Source 0 ,ntity that supplies data to the system

Sin 0 ,ntity that receives data rom the system



"ule% SourceSin

#ust be connected to a process by a data fow



SourceSin% &orrectncorrect?

XX



"ules or 1sing DFD Symbols

Data Flow 2hat &onnects

YES 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



List the errors of this DFD

X3 X5

X4

X2

X1



&ontext Diagram

2op3level view o S

Shows the system boundaries. external entities

that interact with the system. and ma4or

inormation fows between entities and the system-

,xample% 5rder system that a company uses to

enter orders and apply payments against a

customer6s balance



Context Diagram

of Order System



!evel37 DFD

Shows the system6s ma4or processes. data fows.

and data stores at a high level o abstraction

When the &ontext Diagram is expanded into DFD

level37. all the connections that fow into and out

o process 7 needs to be retained-



Leel!" DFD of

Order System



!ower3!evel Diagrams

*n iterative process o breaing a system

description down into 8ner and 8ner detail

1ses a series o increasingly detailed DFDs to

describe an S