Data flow diagrams GapFill

We can visualise how data flows around a system using a data flow diagram (DFD).

Level  3021 diagrams are a very simple way of representing how a system works.

Level  1320 diagrams are much more complex and show specific flows, entities and subprocesses.

There are specific symbols and rules used when drawing Level 1 DFDs.

 An external entityA processAn internal entityA store is an object that enters the system from outside, such as the input of orders received from an online sales platform.  A storeA processAn internal entityAn external entity is an important function of a system, where the data is changed and modified – and displayed or outputted, such as on a screen or in a written report.  An internal entityAn external entityA processA store of data is when it is written to disk after being processed; for example, as a file or as an entry in a database.  An internal entityAn arrowAn external entityA flow of information is the movement of data between each of the external entities, stores and processes, and is indicated on the diagram as   a linea roundrectan arrowa rectangle.

Rules include:

• To  removeconnectinternaliseseparate to the system and transmit data, external entities must have one or more of either an input or an output.
• Each data flow can only go in  onetwozeroten direction(s). If there is an input and an output from an external entity, for example, the data is different for each flow and travels in a different direction, and they must be represented  similarlytogetherseparatelyalternately.
• Data must flow  dependently fromtofromindependently from each process (otherwise there is nothing to process). Data must flow  outdependentlytogetherindependently from a process – the result of processing. Each flow must also be  anonymousdependentindependentlabelled.

Data might not flow through a system as  quicklyslowlyparallelsteadily as expected; for example, a server might be down. This could either cause a delay in that part of the system, or cause large parts of the system to  work correctlyfailrunbe networked.