Lecture on Data Flow Diagrams (DFDs)

Introduction to DFDs

• DFDs stands for Data Flow Diagrams.
• Used in reports and planning stages of systems to show data use and movement.
• Illustrate how data flows around a computer system.

Common Symbols in DFDs

• Process Box: Represents what is using the data or what is being done with the data.
  • Can represent computer systems or human processes.
• External Entity: Objects that provide or receive data (often humans).
• Data Store: Where data is held, such as a database or file.
  • Usually a recognizable shape, like a rectangle missing an edge.
• Arrows: Indicate the flow of data between components.

Types of DFDs

Level 0 DFD

• Provides a high-level overview of a system.
• Example: Backup system with entities like IT Technicians, File Managers, Databases.
  • Shows the basic data flow and interactions (e.g., backup requests, file transfers).

Level 1 DFD

• More detailed and specific than Level 0 DFDs.
• Example: Extended the backup system with detailed process boxes.
  • Includes components like web clients, file transfer programs, and email confirmation systems.
• More detailed breakdown of processes and data flow.

Rules for Creating DFDs

• External Entities: Must have at least one input or output.
• Processes: Must have at least one input and one output.
  • Should not be isolated; always needs connections.
• Data Flow Direction: Should flow in one direction in Level 1 DFDs.
  • Avoid double arrows to ensure clarity.
• Labeling: Every data flow should be labeled.
• Connections: Every data flow must connect to at least one process.
  • Avoid direct connections between entities without a process or data store intermediary.

Exam Tips

• Likely to interpret rather than create DFDs from scratch.
• Recognize symbols and follow the flow of data.
• Understand and identify adherence to the rules in Level 1 DFDs.