Data Flow Diagrams (DFDs)

Introduction

• Purpose: Illustrates how data is processed by a system in terms of inputs and outputs.
• Focus: Flow of information—where data comes from, where it goes, and how it gets stored.
• Historical Context: Became popular in the 1970s, first described by Larry Constantine and Edie Jordan in structured design.

Types of DFD Notations

• Jordon and Coad (Yordan and Coad):
  • Used for system analysis and design.
  • Processes depicted as circles.
• Gane and Sarson:
  • Common for visualizing information systems.
  • Processes depicted as squares with rounded corners.

Common Symbols and Notations

1. Process Notation:
   • Transforms incoming data flow into outgoing data flow.
2. Data Store Notation:
   • Repositories of data in the system, sometimes called files.
3. Data Flow Notation:
   • Lines through which packets of information flow, labeled with the data name.
4. External Entity Notation:
   • Objects outside the system that communicate with it.
   • Sources and destinations of system's inputs and outputs.

Levels or Layers of DFDs

• Context Diagram (Level 0):
  • Top-level diagram with one process node (Process 0).
  • Generalizes the function of the entire system in relation to external entities.
• Level 1:
  • More detailed analysis of data in the context diagram.
• Level 2 and Beyond:
  • Further breakdown of processes, leading to pseudocode.
  • Pseudocode is informal coding language for human reading.

Constructing DFDs

• Tools: Automated diagramming tools like SmartDraw.
  • Provides symbols and templates for easy construction.
  • Features like drag-and-drop and typing for data entry.
  • Allows nesting of different levels using hyperlinks.

Additional Resources

• How-To Video: Demonstrates building a DFD from start to finish.

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Conclusion

• Data flow diagrams are valuable tools for visualizing the flow and processing of data within systems.
• They assist in system analysis and design before implementation.