Data flow diagrams

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Data flow diagrams
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Data flow diagrams are a tool for the description, analysis and design of information systems, whose origins date back to the first generation of information systems (transactional systems, batch systems).

In a graphic way, they present the basic relationships occurring in information processes, the advantage of which is the maximum simplification of the symbolism used. There are only 4 symbols, meaning: process, data warehouse, flow, terminator. The symbolism proposed by Youdon-DeMarco is presented in the figure below.

Data flow diagram.gif Fig. Symbolism used in data flow diagrams

Preparation rules

Using the data flow diagrams, there are a few rules to keep in mind:

  • there are no procedures (processes) of beginning and end,
  • there are no loops or decision blocks,
  • you should use unique names of processes and flows (it is useful to number them),
  • naming flows to and from the data store is not suitable
  • flow between data stores and between terminators is unacceptable,
  • the data warehouse should be used for at least two processes,
  • an arrow towards the data warehouse means that specific changes are made (introduction, update, deletion),
  • an arrow from the data store means that the data is read,
  • the diagram can describe automated and manual flows,
  • the diagram can be created at various levels of detail.