Data Flow Diagram

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Data Flow Diagram

• Keng Siau
• Department of Management
• University of Nebraska-Lincoln

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Data Flow Diagram

• A structured analysis technique
• Graphically characterize data processes and flows
  in a business system
• how data flows through the organization
• the processes or transformation that the data
  undergoes
• what the outputs are
• Emphasize the logic underlying the system

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DFD for Requirements Determination- Advantages

• Not committed to technical implementation of the
  system
• Conceptual understanding of the inter-relatedness
  of systems and subsystems
• Communication with end users
• Analysis of proposed system
• defining data and processes

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DFD Conventions

• External Entity
• Data Flow
• Process
• Data Store

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External Entity

• Origin and/or destination of the data
• Can send data to or receive data from the system
• Outside the system we are studying
• Examples
• a department
• a business
• a person

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Data Flow

• Movement of data from one point to another
• Examples
• data on a customer order form or a payroll check
• results of a query to a database
• content of a printed report

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Process

• Work or actions performed on data so that they
  are transformed
• Data flow leaving a process is always labeled
  differently from the one entering it
• Examples
• compute income tax
• add customer record
• print report

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Data Store

• A depository for data
• Can be a tape, a diskette, a filing cabinet
• Examples
• customer files
• sales files

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DFD Constructs- Naming Guidelines

• External Entity -- gt Noun
• Data Flow -- gt Names of data
• Process
• a system name
• a subsystem name
• a verb-adjective-noun format
• Data Store -- gt Noun

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Guidelines for Developing DFD

• Make a list of business activities
• Use the list to determine various
• external entities
• data flows
• processes
• data stores

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Guidelines for Drawing DFD

• Create the Context Diagram
• shows external entities and data flows to and
  from the system
• Create Diagram 0
• shows general processes at the highest level
• Create Child Diagram
• shows more detailed processes