Definitions
link network
a network in which vertices are perfectly reliable, and only links may fail.
ordinary networka network in which vertices as well as links may fail. A network can be regarded as a link network, or an ordinary network depending on vertices being perfect or not.
variablea variable is a link or a vertex.
essential variablea variable other than source or sink vertices of a network, whose failure has the dominating effect on network reliability.
inverted edgean edge in a BDD; and the binary value at the terminal node of a BDD is complemented if an inverted edge is followed.
overheadthe time penalty incurred when perfect vertices in a network are treated as imperfect.