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Data Flow Diagrams (DFD)

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Data Flow Diagrams (DFD) DFDs are about depicting the movement of data in an information system. Synonyms of DFDs are bubble chart, process model, and transformation ... – PowerPoint PPT presentation

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Title: Data Flow Diagrams (DFD)


1
Data Flow Diagrams (DFD)
  • DFDs are about depicting the movement of data in
    an information system.
  • Synonyms of DFDs are bubble chart, process model,
    and transformation graph.
  • DFDs have four symbols data flows, processes,
    data stores, and external entities (entities).

2
DFD Symbols
Descriptive singular nouns Examples Registrar
Suppliers MS Manufacturing System
FIS Financial Info. System
A strong action verb object clause that defines
what the work is being performed on (or
for) Examples Validate Student Information
Process Customer Order Calculate Order
Cost Check Customer Credit Create
New Member Account
3
DFD Symbols
Avoid physical names such as file cabinets,
database file, etc. Examples Orders
Members Accounts Receivables
  • Descriptive nouns and noun phrases that are
    singular.
  • Should be unique
  • Use adjectives and adverbs to describe how
    processing changed data flow
  • Examples Employee address
  • Membership application
  • Accepted order

Data Flows
4
Process
  • A process is used to transform an input to an
    output.
  • We are interested in WHAT work or action is being
    performed (Logical Design) and not on WHAT or WHO
    is doing that activity (Physical Design)
  • The physical implementation of the system are not
    shown in a DFD.

5
Data Flows
  • Data flows show inputs of data to a process, or
    the outputs of data from a process.
  • In addition, data flows are used to create,
    delete, or update of data in data storage.
  • Telephone calls, business forms, Web forms,
    reports, may create data flow(s).
  • We are not interested in physical data flows.

6
Data Flows
  • Do not leave any data flow unnamed. If you cannot
    give a data flow a reasonable name, it probably
    doesnt exist!
  • Data flow names should describe the data flow
    without describing how the flow is or could be
    implemented.
  • All data flows must begin or end at a process
    because data flows are inputs and outputs of a
    process.

7
External Entities
  • Define the boundary of the information system and
    shows places where the system interfaces with its
    environment.
  • Defines an organizational unit, a person, or
    other organization that lies outside the scope of
    the project, but that interacts with the system.
  • Provides input and receives output.
  • You may duplicate external agents on DFD to avoid
    crossing data flow lines.

8
Data Store
  • A business needs to store data about
  • Persons Agency, Contractor, Customer.
  • Places Sales region, Building, Room.
  • Objects Book, Machine, Part.
  • Events Application, Class.
  • Concepts Account, Bond, Fund.
  • You may duplicate data stores on a DFD to avoid
    crossing data flows lines (max. 3 duplications
    advised).

9
Context Diagram(Level 0 Diagram)
  • Shows the scope of the IS project.
  • Shows systems interaction with the external
    environment.
  • Includes only one process.
  • Includes only external data stores.
  • External data stores can not be changed
    (read-only).

10
Student Registration System Context
11
Student Registration System DFD
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15
Common Errors
Input not sufficient to produce this output A
Gray Hole
No Output A Black Hole
No Input A Miracle
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