1. Data Flow Diagrams
Objectives:
• To define what is meant by structured analysis
• To define the symbols used in a Data Flow
Diagram (DFD)
• To draw a context diagram (Level 0 DFD) for a
given scenario
• To refine a DFD to a more detailed (lower-level)
view

2. Structured analysis
•A widely-used top-down method for defining
system inputs, processes and outputs.
•It shows how information flows through a
system, using several diagrams showing
progressively more and more detail at each
level.
•The primary tool of structured analysis is the
Data Flow Diagram (DFD).

3. Data Flow Diagrams
The following four symbols are used in data
flow diagrams:
External entity
Process
Data store
Data flow

4. Data flow diagram of a travel
agent booking system
Customer
Travel-query
Available flights
flights
Book
flight
Booking
confirmation
Booking

5. Data flow diagram of part of an
order processing system
Order
Available stock
Customer
Invoice
stock
Process
order
Unfilled order
Out-of-stock notice
Despatch note
Warehouse
backorders

6. Context diagrams
a top-level DFD shows the least amount
of detail and is known as a Level 0 DFD
or context diagram.
Order
Customer
Invoice
Out-of-stock notice
Order rejection
notice
Process
order
Picking List
Warehouse

7. • Level 0 or context diagram shows a
system as a single process with inputs
and outputs flowing to or from external
entities.
• Level 1 DFD will split up that single
process into subsystems and show
more detail about the data flows and
data stores.
• Level 2 DFD may decompose a single
subsystem even further.