There are four components for a Data Flow Diagram. They are
External Entities/ Terminators are outside of the system being modeled.
They represent where information comes from and where it goes. These
are represented by rectangles.
Processes, usually represented by an ellipse (circle), which modify the
input to generate the output.
Data Stores represents a place in the process where data rests. This is
represented by an open-ended rectangles or a cylinder symbol.
Data Flows, represented by arrows, are how data moves between
terminators, processes, and data stores