Constraints may be added to the causes and effects. These are represented as edges labelled with the constraint symbol using a dashed line. For causes, valid constraint symbols are E (exclusive), O (one and only one), and I (at least one). The exclusive constraint states that both causes1 and cause2 cannot be true simultaneously. The Inclusive (at least one) constraint states that at least one of the causes 1, 2 or 3 must be true. The OaOO (One and Only One) constraint states that only one of the causes 1, 2 or 3 can be true.
For effects, valid constraint symbols are R (Requires) and M (Mask). The Requires constraint states that if cause 1 is true, then cause 2 must be true, and it is impossible for 1 to be true and 2 to be false. The mask constraint states that if effect 1 is true then effect 2 is false. (Note that the mask constraint relates to the effects and not the causes like the other constraints.
The graph's direction is as follows: (XXX: a figure would represent this better)
Causes --> intermediate nodes --> Effects
A cause-effect graph is useful for generating a reduced decision table.