Symbols used in DFDs


Symbols used in DFDs


Processes:
  • must have at least one input and at least one output
  • at the primitive level (see below for primitive DFD) are labeled with verb + object (e.g. “print invoice” or “add customer”) (e.g. in the hierarchy below, none of the processes are primitive)
  • at the non-primitive level, are labeled more generally (e.g. “customer maintenance” or “warehouse reports”)
Data stores:

  • Data stores can be online or “hard copy” (see notes on logical VS physical DFDs)
  • Data stores will labeled with a noun (e.g. the label “customer” indicates that information about customers is kept in that data store)
  •  Data is stored whenever there are more than one process that needs it and these processes don’t always run one after the other (if the data is ever needed in the future it must be stored.)


Entities/Sources:

  • can be people, departments, other companies, other systems…
  • are called sources if they are external to the system and provide data to the system, and sinks if they are external to the system and receive information from the system

Data flows:
  • must originate from and/or lead to a process (this means that entities and data stores cannot communicate with anything except processes –remember that it takes a process to make the data flow)
  • can go from process to process, but that does imply that no data is stored at that point
  • can have one arrowhead indicating the direction in which the data is flowing
  • can have 2 arrowheads when a process is altering (updating) existing records in a data stores.


Common mistakes while creating DFDs

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