Data Flow Diagrams Example

System Analysis and Design/ Tools for systems analysts

Learning Objectives

Learning Objectives

What are Data Flow Diagrams (DFDs)?
Why they are useful?
How are they developed?
How to level DFDs?
Good style conventions in developing DFDs
Difference between Logical and Physical DFDs
Tools available to draw DFDs

V. Rajaraman/IISc. Bangalore

//V1/June 04/1

System Analysis and Design/ Tools for systems analysts

Motivation

Motivation

WHY DFD ?
Provides an overview of
-What data a system processes
-What transformations are performed
-What data are stored
-What results are produced and where they flow
Graphical nature makes it a good communication tool between
-User and analyst
-Analyst and System designer
Structure of DFD allows starting from a broad overview and expand it to a hierarchy of detailed diagrams

V. Rajaraman/IISc, Bangalore

//V1/July 04/1

DATA FLOW
DIAGRAMS
WHAT ARE DATA FLOW DIAGRAMS?
DFDs models the system by depicting
• External entities from which the data flows and where results terminate
• Processes which transform data flows
• Data stores from which the data are read or into which data are written by the processes.
V.Rajaraman

M5/LU1/V1/2004

5

SYMBOLS USED IN DFD
PROCESS
Stores demand note 1.
STORES Issue Advice

Delivery slip

• A circle represents a process
• Straight lines with incoming arrows are input data flows
• Straight lines with outgoing arrows are output data flows
• Processes are given serial numbers for easy reference
• Labels are assigned to Data flow.These aid documentation
V.Rajaraman

M5/LU1/V1/2004

2

SYMBOLS USED IN DFD
EXTERNAL ENTITIES

VENDOR

Invoice

Order
Customer
Bill

• A Rectangle represents an external entity
• They either supply data or receive data
• They do not process data

V.Rajaraman

M5/LU1/V1/2004

3

SYMBOLS USED IN DFD
DATA STORES
Inventory

Writing

Reading

• A Data Store is a repository