Computing the probabilities of the top event fro the ROBDDs

The fault trees can be very economically encoded by means of ROBDDs. Besides that it is well known that the probabilities of the top event can be computed from the ROBDD encoding the initial fault tree by simple recursive algorithm. It is our intention to show that it is possible to get different kinds of approximations of the probability of the top event when the ROBDD representation is used for the minimal cut set. In our test examples we will show that these differences can be significant, and that this type of calculations should be taken carefully.