Data Flow Diagrams

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