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Data Flow Diagrams
Objectives:
• To define what is meant by structured analysis
• To define the symbols used in a Data Flo...
Structured analysis
•A widely-used top-down method for defining
system inputs, processes and outputs.
•It shows how inform...
Data Flow Diagrams
The following four symbols are used in data
flow diagrams:
External entity
Process

Data store
Data flo...
Data flow diagram of a travel
agent booking system

Customer

Travel-query

Available flights
flights

Book
flight
Booking...
Data flow diagram of part of an
order processing system
Order

Available stock

Customer
Invoice

stock

Process
order
Unf...
Context diagrams
a top-level DFD shows the least amount
of detail and is known as a Level 0 DFD
or context diagram.
Order
...
• Level 0 or context diagram shows a
system as a single process with inputs
and outputs flowing to or from external
entiti...
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Data flow diagrams

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Data flow diagrams

  1. 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. 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. 3. Data Flow Diagrams The following four symbols are used in data flow diagrams: External entity Process Data store Data flow
  4. 4. Data flow diagram of a travel agent booking system Customer Travel-query Available flights flights Book flight Booking confirmation Booking
  5. 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. 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. 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.

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