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Data Flow Diagrams (DFD) are graphical representations of the flow of data through an information system. They are related to document and system flowcharts and can incorporate them, but differ from them in lacking loops and decision points.
Together, these tools offer utility to various specialists working with data. Some examples include:
- A systems analyst may use flowcharts to identify shortcomings in existing information systems and communicate proposed changes to other specialists.
- A systems designer can use them to document his or her design, create instructions on its implementation, and communicate with other specialists.
- Computer programmers can use diagrams while working on a software solution to chart its internal structure and coordinate with their co-workers.
- An auditor uses flowcharts to visualize complex data, find possible issues, and identify their source.
- A data security expert can assess data flows represented in a diagram form to identify vulnerable links in the system and describe processes aimed at fixing those vulnerabilities.
Designing clear and informative flowcharts requires adherence to certain principles, which can be applied to DFDs, document and system flowcharts. These principles include using appropriate and consistent symbols, following a consistent naming scheme with unique names and numbering across diagrams, ensuring consistent flow direction, and branch direction. For presentation, consistent element size, spacing, and a limited color scheme that reduces visual noise, are crucial. Ideally, a chart should be organized to fit on a single page, linking to other diagrams if necessary. Finally, including a legend section and footnotes can help avoid ambiguity.
DFDs typically consist of four symbols, whose visual representation varies across notations, but they represent the same concepts:
- Data storage, such as a computer file or a physical cabinet.
- Process, which describes data being changed between an input and an output.
- External entity that can receive or output data, but the designer has no control over them (Rajaraman, 2018).
- Data flow between the other three elements.
DFDs are designed in a hierarchical structure for clarity since a single diagram describing an entire system in detail is impractical and difficult to read. Splitting the representation into separate diagrams allows a quick overview of the system at higher levels, or finer detail at sequentially lower levels. This hierarchy starts from a level 0, top level, or context diagram, which represents the entire system with a single process (Tilley & Rosenblatt, 2016). The process in this diagram can be expanded into a level 1 diagram representing parts of it in greater detail, then expanded further into a level 2 diagram, and further, exposing more detail as necessary.
Rajaraman, V. (2018). Analysis and design of information systems (3rd ed.). New Delhi, India: PHI Learning Private Limited.
Tilley, S., & Rosenblatt, H. J. (2016). Systems analysis and design (11th ed.). Boston, MA: Cengage Learning.