Data Flow Diagram Notations

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Data Flow Diagram Notations
DataflowDataflows are pipelines through which
packets of information flow. Label the arrows
with the name of the data that moves through it.
Data StoreData stores are repositories of data
in the system. They are sometimes also referred
to as files.
ProcessA process transforms incoming data flow
into outgoing data flow.
External EntityExternal entities are objects
outside the system, with which the system
communicates. External entities are sources and
destinations of the system's inputs and outputs.
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DataFlow Diagrams
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Data Flow Diagram LayersDraw

• Data flow diagrams are drawn in several nested
  layers
• A single process node on a high level diagram
  can be expanded to show a more detailed data flow
  diagram.
• Draw the context diagram first, followed by
  various layers of data flow diagrams.

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DFD Layers
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Context Diagrams

• A context diagram is a top level (also known as
  Level 0) data flow diagram. It only contains one
  process node (process 0) that generalizes the
  function of the entire system in relationship to
  external entities.

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DFD levels
The first level DFD shows the main processes
within the system. Each of these processes can be
broken into further processes until you reach
pseudocode.
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Context Diagram- Registration
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Level 0 Data Flow Diagram
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Explosion of Process 4
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Level 0 DFD ATM
User
request
Transaction requests
member banks
ATM
display
Balance Information
receipt
Printer
Account data
Information request
account database
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A level 1 DFD
Printer/display
Customers Card details
Rejection message
1. Validate Customer access
2. Reject transaction \and end session
Access map
PIN
Access authorization
Network directory
customer
Rejection message
3. Obtain Details of transaction
Access permissions
4. Validate transaction
select options
Transaction request
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A level 2 DFD
Customers Card details
Cannot Read card
1.1 Read Details From card
Printer/display
Card data
Encoded pin
1.2 Check Expiry date And bank group
customer
1.3 Request Pin And match Max 3 attempts
PIN
Card Validation data
Access map
Invalid pin
Access authorization
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Another Approach to the ATM Level 1
Get deposit
Get inquiry
member banks
User
bank name
error
error
account
account deposit
account display
Validate inquiry
account
Printer
Do deposit transaction
Create account summary
account data