Data Flow Diagrams DFD

1
Data Flow Diagrams (DFD)

• Context diagram
• Top-level diagram, shows links with environment
• Physical flow diagram
• Shows persons, places, things that transform data
• Internal entity part of system transforming the
  data
• External entity sources or destinations of data

2
Data Flow Diagrams (DFD)

• Logical data flow diagram
• Shows process and flow of data
• Systems flow charts
• Information processes and operations processes

3
Data Flow Diagram (DFD) Symbols
NOTES a. A bubble can be either an entity on a
physical data flow diagram or a process on a
logical data flow diagram. b. The data store
symbol may represent a viewa portionof a larger
entity-wide database.
FIGURE 2.1
4
A Context Diagram
FIGURE 2.2
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A Physical Data Flow Diagram
FIGURE 2.3
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A Logical Data Flow Diagram (Level 0 Diagram)
FIGURE 2.4
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Causeway Context Diagram
FIGURE 2.10
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Causeway Current Physical DFD
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Causeway Current Logical DFD (Level 0)
FIGURE 2.12
10
Drawing DFD Diagrams

• The basic steps of the process are
• Create or obtain an accurate and reliable
  narrative.
• From the narrative, create a complete table of
  entities and activities.
• Draw a context diagram with external entity boxes
  (distinguish between internal and external
  entities).
• Draw current physical flow diagrams by creating
  bubbles for internal entities, and showing flows
  to and from all entities and data stores.
• Draw current logical flow diagrams by grouping
  activities that occur together, and naming the
  logical sub-processes each describes.

11
Flowcharting

• Setup columns for each internal entity
• Use narratives and DFDs as source of information
• Show activities left to right and top to bottom
• Use appropriate symbols for all processing
  (manual and computer)
• Balance between clarity and clutter
• Compare finished flowchart to narratives and DFDs
  to ensure completeness