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DFD

DFD. Process modeling. To do tonight. 1. Learn to draw DFDs 2. Understand what does not belong in DFDs 3. Learn DFD Rules and Conventions. What DFD is?. A DFD is a network representation of a system. The system may be computerized, manual, or a hybrid of the two.

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DFD

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  1. DFD Process modeling

  2. To do tonight.. 1. Learn to draw DFDs 2. Understand what does not belong in DFDs 3. Learn DFD Rules and Conventions

  3. What DFD is? • A DFD is a network representation of a system. The system may be computerized, manual, or a hybrid of the two. • The DFD portrays the system in terms of its component pieces, with all interfaces among the components indicated • DFDs should not show flow of control or control information • DFDs are not really flow diagrams in the traditional sense--they are a tool for functional decomposition

  4. DFDs-- Four notational symbols

  5. Reading Data Flow Diagrams

  6. Identifying Processes • Direct Identification • Top-Down • Bottom-Up • Outward-In • Functional Sequence

  7. Identifying Data Stores • Examine Nouns • Identify significant ‘things’ about which you need to store information • Avoid description in terms of physical devices • Data Store =>e.g. “Applications” ¹ Bill’s File

  8. DFD: Conventions - Processes • Process names should be descriptive. • Processes should have a single Action Verb and a Singular Object. Tip: Name data flows before naming Processes.

  9. DFD: Conventions - Data Flows • Names reflect not only data which moves, but what we know about the data.

  10. DFD: Common Mistakes

  11. DFD: Common Mistakes

  12. DFD: Common Mistakes

  13. DFD: Common Mistakes • Black Holes and Miracles

  14. DFD: Balancing and Leveling

  15. Working toward a leveled set of DFDs

  16. Working toward a leveled set of DFDs

  17. Stopping • When do we stop creating more levels? – Each Process performs only ONE function • Signs indicating need to partition further: – process is difficult to name – has too many inputs or too many outputs – would be easier to understand if broken down

  18. Signs of Errors • Leveling/Balancing Errors • Deceptive Process Labels • Flow of Control Information • Too many data flows • Never-used Inputs • Widely varied depths of explosion

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