DFD

A data flow diagram (DFD) is a graphical tool used to illustrate how data moves through an information system, how it is processed, stored, and externalized. DFDs focus on the flow of information rather than the sequence of operations, making them useful for understanding system boundaries and data interactions during analysis and design.

A DFD depicts four basic elements: processes, data stores, data flows, and external entities. Processes represent operations that transform data. Data stores hold data persistently for later use. Data flows show the movement of data between processes, stores, and external entities. External entities are sources or destinations of data outside the system being modeled. DFDs commonly use a hierarchy of diagrams, starting with a context diagram (level-0) that shows the system as a single process with its external interfaces, followed by Level-1 and deeper diagrams that decompose processes into sub-processes. Notation variants include structures such as Gane-Sarson and Yourdon–DeMarco, differing mainly in symbol shapes.

Construction typically involves scope definition, identification of external entities, processes, stores, and data flows, drawing the context diagram, and iterative decomposition into lower levels while applying consistency rules, such as balancing data flows across levels. DFDs are widely used in requirements gathering, system analysis, and design documentation to improve communication among stakeholders and reveal data dependencies.

Limitations include a lack of timing, control flow, and data attribute details, and the potential for oversimplification or complexity if not carefully scoped. DFDs complement other modeling approaches, such as flowcharts, ER diagrams, and UML activity diagrams, by emphasizing data movement and transformation.