Systems Analysis and Design – DFD Overview
Data Flow Diagrams (DFD)
Data Flow Diagrams (DFDs), as the name suggests, illustrates the
flow of information in a system. DFDs are hardware independent
and they do not reflect decision points. Rather they demonstrate
the information and how it flows between specific processes in a
system. They provide one kind of documentation for our reports.
Naming Conventions used follow Gane and Sarson Notation:
Data Flows: name of the packet of information (arcs)
Data Stores: name of the data stored there (rectangle)
Transformations: name of the activity (bubbles)
Origins and Destinations: name of producers, customers, etc. in
the environment (boxes)
Since they generally describe a complex system, there are layers
of DFD's that show increasingly more information about the
processes. Consider the diagram below.
Systems Analysis and Design – DFD Overview
By Mansha Nawaz
1
Systems Analysis and Design – DFD Overview
These diagrams show a group of related sets:
Context Diagram: This is the highest level and represents the
overall system and its interaction with its environment
Systems Analysis and Design – DFD Overview
By Mansha Nawaz
2
Systems Analysis and Design – DFD Overview
Level 0 Diagram: This shows the major subsystems and their
interactions
Level x Diagram: Shows the processes that make up each of the
major subsystems
Level x.y Diagram: Shows detail of the above diagrams
Each bubble on one level gets "exploded" to show the detail at
another level. These pairs are referred to as parent-child pairs. It is
important to keep balance between the individual parents and their
children.
Numbering: Each process in Level 0 gets a number. Each child
inherits the number. Bubbles on the child dfd maintain that
number, and begin their numbering as a number after the decimal
point. These are unique numbers.
Systems Analysis and Design – DFD Overview
By Mansha Nawaz
3
Systems Analysis and Design – DFD Overview
Numbering: Each process in Level 0 gets a number. Each child
inherits the number. Bubbles on the child dfd maintain that
number, and begin their numbering as a number after the decimal
point. These are unique numbers.
When to stop:
Each process is a single decision or calculation or a single
database operation, such as retrieve, update, create, delete or
read.
Each data store represents data about a single entity such as a
customer, employee, product or order.
The system user does not care to see any more detail or when you
and other analysts have dcoumented sufficient detail to do
subsequesnt systems development tasks.
Every data flow does not need to be split further to show that
different data are handled in different ways.
You believe that you have shown each business form or
transaction, computer screen and report as a single data flow.
You believe there is a separate process for each choice on all
lowest-level menu options for the system.
Class Examples of the Registration Process:
Data Flow Diagram (DFD) Example (Context Diagrams).
Data Flow Diagram (DFD) Example (DFD Level 0 Diagrams).
Data Flow Diagram (DFD) Example (DFD Level 4 Explosion).
Data Dictionary Example (Data Repository).
Systems Analysis and Design – DFD Overview
By Mansha Nawaz
4
Systems Analysis and Design – DFD Overview
Data Flow Diagram (DFD) Example (Context Diagrams).
These examples demonstrate the flows of information for the
registration process.
Context Diagram. : Registration Process
Systems Analysis and Design – DFD Overview
By Mansha Nawaz
5
Systems Analysis and Design – DFD Overview
Data Flow Diagram (DFD) Example (DFD Level 0 Diagrams).
The second of these is the Dataflow Diagram Level 0 Diagram
These examples demonstrate the flows of information for the
registration process.
DFD Level 0: Registration Process
Systems Analysis and Design – DFD Overview
By Mansha Nawaz
6
Systems Analysis and Design – DFD Overview
Data Flow Diagram (DFD) Example (DFD Level 4 Explosion).
This page illustrates the explosion of Process 4, Enroll Students.
DFD Level 1: Enroll Students
View some sample data repository items associated with this diagram.
Systems Analysis and Design – DFD Overview
By Mansha Nawaz
7
Systems Analysis and Design – DFD Overview
Data Dictionary Example (Data Repository).
Data Repository Examples
Process
4.6
Systems Analysis and Design – DFD Overview
By Mansha Nawaz
8
Systems Analysis and Design – DFD Overview
Data
Store
Systems Analysis and Design – DFD Overview
By Mansha Nawaz
9
Systems Analysis and Design – DFD Overview
Data
Flow
Systems Analysis and Design – DFD Overview
By Mansha Nawaz
10