DFD LEVEL -1: source/sinks and data store are allowed to included?



  • I am trying to develop a DFD level 0 and 1. But as I learned from different sources(eg. textbook, website) that some say data store and sources/sinks are not allowed in the level-1 and the rest of decomposed diagrams, but some say it can be.

    Are there any criteria for DFD decomposing development?

    Thanks



  • It's not that easy to find something useful about it online, I agree. Accordingly to Timothy Arndt and Angela Guercio in Decomposition of data flow diagrams,

    Data flow diagrams are an important design aid in system development.

    and

    Decomposition is the top-down development of a data flow diagram starting with the system inputs and the system outputs

    Personally I liked the content from Visual Paradigm on the matter to know more about DFD. About decomposition, they write

    Top-down decomposition, also called leveling, is a technique used to show more detail in lower-level DFDs. Leveling is done by drawing a series of increasingly detailed diagrams until the desired degree of detail is reached.

    In other words, when doing leveling the goal is

    first displaying the targeted system as a single process, and then showing more detail until all processes are functional primitives.

    When you ask in your question

    some say data store and sources/sinks are not allowed in the level-1 and the rest of decomposed diagrams, but some say it can be

    what i extract from that article in Visual Paradigm is that in a context diagram you don't want any data source but in a Level 1 it's fine (there's even one example of it there - see next image).

    enter image description here

    In fact, there's some considerations / criteria to have for DFD leveling: unique names for levels, no cross line, numbering convention, ...

    I suggest you to have a look as well at this article from Visual Paradigm which explains DFD by using a food ordering system as an example.


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