How do you draw a data flow diagram?

A group of circles for the various processes interconnected by arrows for the various data flows. Usually drawn hierarchal starting with DFD 0, also called the context diagram, containing exactly one circle in the center and rectangles around the edges for the various data sources & data sinks. The remaining DFDs are numbered like an outline.

Its rather obvious when you see an example, but diagrams can't be included here.