This book contains many examples of influence diagrams. The idea of influence diagrams is taken from Gerald Weinberg's excellent Quality Software Management series, particularly Book 1: Systems Thinking. The purpose of an influence diagram is to see how the elements of a system affect one another.
Influence diagrams have three elements:
Activities, notated as a word or short phrase
Positive connections, notated as a directed arrow between two activities; meaning that more of the source activity tends to create more of the destination activity, or less of the source activity tends to create less of the destination activity
Negative connections, notated as a directed arrow between two activities with a circle over it; ...