Combinatorial models, such as fault trees, digraphs and reliability block diagrams, usually use cutset-based techniques for quantitative analysis. Recent research has suggested that the Binary Decision Diagram (BDD) offers an efficient solution alternative. However, combinatorial models by themselves are not sufficient for the analysis of fault tolerant systems unless augmented by a cover-age model, which assesses the effectiveness of the recovery mechanisms incorporated for fault tolerance. In this paper, we describe the DREDD algorithm (Dependability and Risk Evaluation using Decision Diagrams), which effectively combines the BDD solution method for a combinatorial model with the solution of a coverage model. Three example fault tolerant systems are analyzed using DREDD.
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