“…The qualitative approaches involve fault trees (Lees, 1983), signed directed graph (Kramer and Palowitch, 1987), functional decomposition (Finch and Kramer, 1988), fuzzy logic (Vaija, 1985), neural networks (Venkatasubramanian and Chan, 1989), and expert systems (Dhurjati et al, 1987). The quantitative approaches are basically modeling, filtering, and estimation methods.…”