Data Flow Diagram

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12/8/2012

Major Topics
Chapter 9
Using Data Flow Diagrams

Data flow diagram symbols
Data flow diagram levels
Creating data flow diagrams
Physical and logical data flow diagrams
Partitioning
Event driven modeling
Use case and data flow diagrams

Systems Analysis and Design
Kendall and Kendall
Fifth Edition

Kendall & Kendall

Using Data Flow Diagrams

Unexploded data flow diagrams are useful
to identify information requirements
Exploded data flow diagrams can be used
for presentation, education, and gathering
feedback information from users

Copyright © 2002 by Prentice Hall, Inc.

9-3

One of the main methods available for
analyzing data-oriented systems
DFDs emphasize the logic underlying
the system
The systems analysts can put together
a graphical representation of data
movement through the organization
Copyright © 2002 by Prentice Hall, Inc.

DFDs may be used to analyze the
system to ensure that the design is
complete
DFDs are used to partition the system
into programs
Data flow diagrams can be used for the
system documentation
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Copyright © 2002 by Prentice Hall, Inc.

9-4

Advantages of the Data Flow
Diagram Approach

Data Flow Diagrams

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9-2

Using Data Flow Diagrams

Data flow diagrams can be used for
several different purposes:

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9-5

Four advantages over narrative
explanations of data movement
Freedom from committing to the technical
implementation too early
Understanding of the interrelationships of
systems and subsystems
Communicating current system knowledge
to users
Analysis of the proposed system
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Copyright © 2002 by Prentice Hall, Inc.

9-6

1

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Basic Symbols

External Entities

Four basic symbols are
A double square for an external entity--a
source or destination of data
An arrow for movement of data from one
point to another
A rectangle with rounded corners for the
occurrence of transforming process
An open-ended rectangle for a data store
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9-7

External Entities

9-9

Data Stores

computer file or database
transaction file
set of tables
manual file of records

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9-8

A whole system
A subsystem
Work being done, an activity

Names should be in the form verbadjective-noun
The exception is a process that represents
an entire system or subsystem
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9-10

Data Flow

Name with a noun, describing the data
Data stores are usually given a unique
reference number, such as D1, D2, D3
Include any data stored, such as:
A
A
A
A

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Represent either:

A person, such as CUSTOMER or STUDENT
A company or organization, such as BANK
or SUPPLIER
Another department within the company,
such as ORDER FULFILLMENT
Another system or subsystem, such as the
INVENTORY CONTROL SYSTEM
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Processes

External entities may be

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Represent people or organizations
outside of the system being studied
Shows the initial source and final
recipient of data and information
Should be named with a noun,
describing that entity

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Shows the data about a person, place,
or thing that moves through the system
Names should be a noun that describes
the data moving through the system
Arrowhead indicates the flow direction
Use double headed-arrows only when a
process is reading data and updating
the data on the same table or file
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Copyright © 2002 by Prentice Hall, Inc.

9-12

2

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Developing Data Flow
Diagrams

Creating Data Flow Diagrams

Use the following guidelines:
Create the context level diagram, including
all...
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