Data Flow Diagram Concepts

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Data Flow Diagram Concepts

• In a Context Diagram
• One process representing the entire system
• All external entities
• All relevant data flows

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Data Flow Diagram Concepts

• In a Level Zero Diagram
• Expect 5 /- 2 processes
• (Attempt to have all processes at same level of
  abstraction)
• All external entities
• All data stores used by these processes
• All relevant data flows

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Data Flow Diagram Concepts

• Decomposition
• Decompose until process is clear enough that no
  further explanation is needed (functional
  primitive).

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DFD Concepts

• Balancing
• Inputs and outputs from higher level process must
  be reflected in lower-level (decomposed)
  processes. These may be described in greater
  detail in the lower-level diagram.

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Data Flow Diagram Concepts

• What is NOT in a LOGICAL DFD
• dynamics of system behavior
• timing
• control
• particular input/output/storage media

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Data Flow Diagram Concepts

• Watch out for
• Black Holes
• data goes into a process (or data store) but
  doesnt come out
• Miracles
• a process produces output with no input