A data flow diagram (DFD) maps out the flow of information for any process or system. Data flow diagrams were popularized in the late 1970s, arising from the book Structured Design by computing pioneers Ed Yourdon and Larry constantine. The structured design concept took off in the software engineering field, and the DFD method took of with it.
DFD rules and tips.
1.Each process should have at least one input and an output.
2.Each data store should have at least one data flow in and one data flow out.
3.Data stored in a system must go through a process.
4.All processes in a DFD go to another process or a data store.
Data flow diagram levels.
Context Diagram. A context diagram is a top level (also known as "level 0") that generalizes the function of the entire system in relationship to external entities.
DFD Layers. Draw data flow diagrams can be made in several nested layers. A single process node on high level diagram can be expanded to show more detailed data flow diagram. Draw the Context diagram first, followed by various layers of data flow diagrams.
DFD Levels. The first level DFD shows the main process within the system. Each of these processes can be broken into further process until you reach pseudo code.