T his DFD provides an overview of the data entering and leaving the system. It also shows the entities that are providing or receiving that data. These correspond usually to the people that are using the system we will develop. The context diagram helps to define our system boundary to show what is included in, and what is excluded from, our system.
The diagram consists of a rectangle representing the system boundary, the external entities interacting with the system and the data which flows into and out of the system. Figure 9 gives an example of a context diagram.