What is Data flow diagram ?Essentials components and rules of DFD ?

A data flow diagram (DFD) is a graphical representation of the “flow” of data through an information system, modeling its process aspects. A DFD is often used as a preliminary step to create an overview of the system, which can later be elaborated. DFD’s can also be used for the visualization of data processing (structured design).

  • A DFD shows what kind of information will be input to and output from the system, where the data will come from and go to, and where the data will be stored. It does not show information about the timing of process or information about whether processes will operate in sequence or in parallel (which is shown on a flowchart).

They are four components of DFD

  • External Entity
  • Process
  • Data Flow &
  • Data Stores

External Entity

  • Entity can be anything (i.e. person ,S/W or Hardware) entity can be anything which provide data to your software or consume data from your software.
  • Data Stores
  • Data Stores are the internal to the systems ,in context level diagram you connect show the data stores because they are internal to the systems.

Rules of Data Flow

  • Data cannot flow b/w two data stores.
  • Data cannot be flow b/w two entity’s
  • Meaningful naming conventions to data flow.
  • There should be process in the middle of two entities which process data from one entity’s to other entities.
  • No process have only input data flow (black whole) and output data flow (Miracle).
  • There should be process in the middle of two data Stores which process data from one data Stores to other data stores.
  • No Internal Logic should be show like Loop, if else because this is not flow chart .
  • In Order to not keep data uncluttered, you can repeat data stores and data entities.
  • No direct flow of data b/w two entities and two data stores.

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Ashok Dash




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