IDEF0

IDEF0 (pronounced 'eye-deff-zero') provides a formal method of describing processes or systems, using several techniques to avoid the complex diagrams that could result from an attempt at a complete description using other methods.

It originated from Structured Analysis and Design Technique (SADT), which was put into the public domain as a standard for US government contracts. 

The basic diagram element is very simple, using just one box shape to define each activity or process, as illustrated. The four arrow types are Inputs, Controls, Outputs and Mechanisms (ICOM).

IDEF0 diagrams have only 3 to 6 boxes per page, which results in a tall, thin process hierarchy, which can be difficult to understand in its entirety.

IDEF0 requires a fair amount of specialist knowledge to use properly, and people tend to either love it for its rigor or hate it for its detail and difficulty.

See also:

Toolbook chapter: IDEF0