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DFDs

DFDs. Class 11. SDLC. Project Identification & Selection. Project Initiation & Planning. **Analysis**. Logical Design. Physical Design. Implementation. Maintenance. Parts of DFD. External Agent; Source / Sink Data Store Process Data Flow Line. To Model the system.

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DFDs

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  1. DFDs Class 11

  2. SDLC Project Identification & Selection Project Initiation & Planning **Analysis** Logical Design Physical Design Implementation Maintenance

  3. Parts of DFD • External Agent; Source / Sink • Data Store • Process • Data Flow Line

  4. To Model the system • Emphasize process • Identify, hierarchically: • The system • The subsystems/functions of the system • The transactions within a given function

  5. Characteristics of DFD • I-P-O modeling • Leveling of DFDs (explosion) • Balancing of data flows • Shows flow of data not flow of control • Shows set of possible paths (not what causes a path to be taken)

  6. Explosion • Also called Functional Decomposition • An iterative process of breaking the description or perspective of a system down into finer and finer detail. • Context diagram, Level 0 diagram, Level 1 diagrams, etc. • Balancing the levels

  7. What you CAN’T do: • Processes • No input data flow, no output data flow • Data Stores • Data flow directly to another data store • Agents • Data flow directly to another external agent, data flow directly to or from data store • Data Flows • No double arrows, no “break-off” lines defined as something different, no data flow line into another data flow line

  8. Cougar Burger Example • Context Level

  9. Cougar Burger Example • Level 0

  10. Cougar Burger example • Level 1

  11. Identifying DFD parts • Bottom-up and Top-Down

  12. Different types of DFDs • Current vs New

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