Data flow programs :

A DFD can be categorized in the following forms :

Context diagram :

An overview of an organizational system that shows the system boundaries, external entities that interact with the system and major information flows between the entities and the system.
In this diagram, a single process represents the whole system.

First level DFD :

A data flow diagram that represents a system's major processes, data flows, and data stores at a high level of detail.