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| information systems | |
| data management | |
| diagrams | |
| visualization | |
| systems analysis | |
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Data flow diagrams (DFDs) are one of the three essential perspectives of SSADM. The sponsor of a project and the end users will need to be briefed and consulted throughout all stages of a systems evolution. With a dataflow diagram, users are able to visualise in a physical visual form how the system will operate, what the system will accomplish and how the system will be implemented. Old system dataflow diagrams can be drawn up and compared with the new systems dataflow diagrams to draw comparisons to implement a more efficient system. Dataflow diagrams can be used to provide the end user with a physical idea of where the data they input, ultimately has an effect upon the structure of the whole system from order to dispatch to restock how any system is developed can be determined through a dataflow diagram. The components of a data flow diagram (DFD) are:
;Terminators: are outside of the system being modeled. Terminators represent where information comes from and where it goes. In designing a system, we have no idea about what these terminators do or how they do it. ;Processes : modify the inputs in the process of generating the outputs ;Stores: represent a place in the process where data comes to rest. A DFD doesn't say anything about the relative timing of the processes, so a store might be a place to accumulate data over a year for the annual accounting process. ;Flows: are how data moves between terminators, processes, and stores. It is recomended that every page in an DFD contain fewer than 10 components. If a process has more than 10 components, then one or more components (typically a process) should be combined into one and another DFD be generated that describes that component in more detail. Each component should be numbered, as should each subcomponent, and so on. So for example, a top level DFD would have components 1 2 3 4 5, the subcomponent DFD of component 3 would have components 3.1, 3.2, 3.3, and 3.4; and the subsubcomponent DFD of component 3.2 would have components 3.2.1, 3.2.2, and 3.2.3 The original book on DFDs is 'Structured Analysis and System Specification'. Tom DeMarco. Yourdon, Inc., Englewood Cliffs, New Jersey, 1978. For more information on Data Flow Diagrams, please consult [http://www.yourdon.com/strucanalysis/chapters/ch9.html chapter 9 of Ed Yourdon's on-line book, "Just Enough Structured Analysis"]. |
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