1 / 18

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.

sasha-obrien
Download Presentation

DFD

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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

More Related