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Data Flow Diagram Symbols

Data Flow Diagram Symbols. Process Step-by-step instructions. Data flow. External agent. Data store Data at rest. Real-time link. DFD Fragment from RMO Case. DFD Integrates Event Table and ERD. DFD and Levels of Abstraction.

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Data Flow Diagram Symbols

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  1. Data Flow Diagram Symbols Process Step-by-step instructions Data flow External agent Data store Data at rest Real-time link

  2. DFD Fragment from RMO Case

  3. DFD Integrates Event Table and ERD

  4. DFD and Levels of Abstraction • DFDs are decomposed into additional diagrams to provide multiple levels of detail • Higher levels are more general • Lower levels are more detailed

  5. Context Diagrams • DFD that summarizes all processing activity • Highest level view of system • Shows system boundaries • Scope is represented by a single process and outside agents

  6. Context Diagram for Course Registration System

  7. Context Diagram for RMO Customer Support System

  8. DFD Fragments • Represents system response to one event within a single process symbol • Self contained model • Focuses attention on single part of system • Shows only data stores required to respond to events

  9. DFD Fragments for the Course Registration System

  10. Event Partitioned System Model • DFD that models system requirements using a single process for each event in a system or subsystem • Sometimes called diagram 0 • Decomposition of the context level diagram • Is decomposed into more detailed DFD fragments

  11. Relationships Among DFD Abstraction Levels when Subsystems are also Defined

  12. RMO Subsystem DFD

  13. Event-Partitioned Model of the Order-Entry Subsystem

  14. Decomposing DFD Fragments • Sometimes DFD fragments need to be explored in more detail • Broken into subprocesses with additional detail • Numbering scheme doesn’t equate to execution sequence

  15. Detailed Diagram for Create New Order

  16. Physical and Logical DFDs • Logical model • Assumes implementation in perfect technology • Does not tell how system is implemented • Physical model • Describes assumptions about implementation technology • Developed in last stages of analysis or in early design

  17. Physical DFD for Scheduling Courses

  18. DFD Quality • Readable • Internally consistent • Accurately represents system • Reduces information overload • Minimizes required number of interfaces

  19. Data Flow Consistency Problems • Differences in data flow content between a process and its process decomposition • Data outflows without corresponding inflows • Data inflows without corresponding outflows • Results in unbalanced DFDs

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