Data Flow Diagram
A data flow diagram (DFD) shows how data moves through a business, automated or manual system, or program.
A DFD can show a high-level or low-level view of a system.
On a data flow diagram, all the processes are at approximately the same level. There should be no more than about ten processes shown on a data flow diagram to avoid showing too much detail on a single page.
Data Flow Diagram Objects
There are different sets of symbols available for data flow diagrams, depending on accepted conventions. The following shows Gane & Sarson's methodology.
process A process is a unit of work that operates on the data. The process may be automated or manual, on-line, batch, or real- time. The symbol for a process is a rounded rectangle.
data flow A data flow is a named flow of data through a system of processes. A data flow is shown as a directed line on the diagram.
data store A data store is a logical repository of data. It may be an automated file, a paper file, etc. A data store is shown as an open-ended rectangle.
external agent An external agent is a source or destination of data. The external agent occurs outside of the system of processes. An external agent is depicted by an overlapping rectangle.

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