DFDs

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DFDs

• Class 11

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SDLC
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Parts of DFD

• External Agent Source / Sink
• Data Store
• Process
• Data Flow Line

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To Model the system

• Emphasize process
• Identify, hierarchically
• The system
• The subsystems/functions of the system
• The transactions within a given function

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Characteristics of DFD

• I-P-O modeling
• Leveling of DFDs (explosion)
• Balancing of data flows
• Shows flow of data not flow of control
• Shows set of possible paths (not what causes a
  path to be taken)

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Explosion

• Also called Functional Decomposition
• An iterative process of breaking the description
  or perspective of a system down into finer and
  finer detail.
• Context diagram, Level 0 diagram, Level 1
  diagrams, etc.
• Balancing the levels

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What you CANT do

• Processes
• No input data flow, no output data flow
• Data Stores
• Data flow directly to another data store
• Agents
• Data flow directly to another external agent,
  data flow directly to or from data store
• Data Flows
• No double arrows, no break-off lines defined as
  something different, no data flow line into
  another data flow line

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Cougar Burger Example

• Context Level

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Cougar Burger Example

• Level 0

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Cougar Burger example

• Level 1

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Identifying DFD parts

• Bottom-up and Top-Down

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Different types of DFDs

• Current vs New