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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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Dfd

DFD

Process modeling


To do tonight

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

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


Dfds four notational symbols

DFDs-- Four notational symbols


Reading data flow diagrams

Reading Data Flow Diagrams


Identifying processes

Identifying Processes

  • Direct Identification

  • Top-Down

  • Bottom-Up

  • Outward-In

  • Functional Sequence


Identifying data stores

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


Dfd conventions processes

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.


Dfd conventions data flows

DFD: Conventions - Data Flows

  • Names reflect not only data which moves,

    but what we know about the data.


Dfd common mistakes

DFD: Common Mistakes


Dfd common mistakes1

DFD: Common Mistakes


Dfd common mistakes2

DFD: Common Mistakes


Dfd common mistakes3

DFD: Common Mistakes

  • Black Holes and Miracles


Dfd balancing and leveling

DFD: Balancing and Leveling


Working toward a leveled set of dfds

Working toward a leveled set of DFDs


Working toward a leveled set of dfds1

Working toward a leveled set of DFDs


Stopping

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


Signs of errors

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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