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Data Flow Diagram (DFD) graphical representation of data
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Data Flow Diagram (DFD)

DFD (Data Flow diagram)

DFD is a graphical presentation of data which let us know the flow of data in a workplace or entity specified. It is used for visualization of data.  It helps us to know the work flow in an organization.  It shows the kind of information to be transferred from one place to another within or out of the workflow, we can also say that DFD’s tells us about the data to be used as input and data to come out as output.

Representation of Components: DFDs can be created using four basic symbols. They are as follows:-

  • Process
  • Data objects
  • Data Store
  • External Entity

Process: Transform of incoming data flow(s) to outgoing flow(s)

Data Flow: Movement of data.
Data Store: Data repositories for data that is stagnant or in other words we can say that it is buffer stock.
External Entity: Sources of destinations outside the specified system boundary.
Logical DFD: A logical DFD shows the flow of data that is necessary for operating a system. It describes the processes that are worked on, the required data and produced by each process and also shows the data that needs to be stored in the database. It captures data flow that is neither redundant nor have any duplication.

Physical DFD- It shows the actual implementation of workflow, either at the moment ( Current Physical DFD) and the expected workflow to be taken into consideration in near future (Required Physical DFD). A Physical DFD will include references to data that are duplicated, or redundant, if implemented as a set of database tables, would constitute an un-normalised relational database.

DFD’s are further explained with the help of various levels in an organization which are explained below:-

  • Level 0
  • Level 1
  • Level 2

The DFD’s may be used at any level for abstraction of data. DFD can be partitioned into levels. Each further level gives an elaborated description of data flows.

Highest level is Context diagram or , Some points to remember are:-

  • 1 bubble represents the entire system.
  • Data arrows show input and output.
  • At this level data stores are not displayed. They are within the system.

Next Level is 1 Level: Some important points to remember are:-

  • Level 1 DFD must balance with the level 0 diagram it describes.
  • Inputs get into the process are different from the output received after the processing of data.
  • Data stores are shown at this level firstly.

Next Level is 2 Level. Some important points to remember are:-

  • Level 2 DFD must balance with the level 1 diagram it describes.
  • Inputs get into the process are different from the output received after the processing of data.
  • Keep going to show data stores.

In same way as above figure showing Record Customer details (Level-2), we can make level-2 DFD for all different sections in project, specifying the requirement , workflow and input – output of data. 

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