8. Conclusion

The very simplicity of BDF makes it a widely used method by engineers in general, and reliability engineers in particular. However, like all other Boolean approaches (fault trees, event trees), BDFs are fraught with mathematical difficulties that are often overlooked by users, and even by certain calculation software programs whose mathematical principles and limitations should always be checked before use. The use of binary decision diagrams solves problems of combinatorial explosion when searching for minimum cuts, and enables analytical calculations of availability or failure frequency without approximation, even when the probabilities involved are high. The combination of BDFs and Markov processes (Markov processes driven by BDFs) is very useful for this purpose. However, except when the components concerned are all non-repairable, exact reliability calculations are not possible. The...