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DFD ​

Data-flow diagram illustrates the flow of information for processes and systems.

Notation ​

  • External entity: Represented by a noun, they are elements outside the system that emits or receive data.
  • Process: Represented by a verb, they are actions that change the data, producing an output.
  • Data Store: Represented by a noun, they are elements that store a type of data, like a table in a database.
  • Data flow: Represented by the name of the data, they are the route between all the others elements.
DFD Process Example

Some rules ​

  • DFD diagrams represent only data, no process, actions or operations…
  • Process and data store always have minimum 2 data flows: in and out
  • All processes must be linked to either another process or a data store.

Levels ​

Level 0 ​

The contextual level is highly abstracted and serve only a resumed overview. It includes:

  • All external entities
  • Only one process
  • No data stores
  • Main data flows Context DFD example

Level 1 ​

The first level highlight main functions of the system by decomposing the main process into subprocesses. Level 1 DFD example

Level 2 ​

The second level take each processes from level 1 and details it into other incremental subprocess (1.x, 2.x, etc.). Level 2 DFD example

You can repeat the process and dig deeper in levels, splitting the process into more details, but 1-2 levels are generally enough.

Resources ​