A DYNAMIC FLOWGRAPH METHODOLOGY APPROACH BASED ON BINARY DECISION DIAGRAMS
Kim Björkman, Ilkka Karanta · 2011
The dynamic flowgraph methodology (DFM) is an approach to model and analyze the behavior of dynamic systems for reliability assessment. The methodology can be utilized to identify how certain postulated top events may occur in a system. The result is a set of prime implicants which represent system faults resulting from diverse combinations of software logic errors, hardware failures, human errors, and adverse environmental conditions. A binary decision diagram (BDD) is a data structure used to represent Boolean functions applied, e.g., in fault tree analysis and model checking. This paper presents an alternative DFM approach based on BDD called YADRAT. The objective of a YADRAT model analysis is to find the root causes of the query (top event) of interest, similarly to traditional fault tree analysis. The main difference of YADRAT compared to the existing DFM approach is that YADRAT employs a BDD to represent a DFM model. Two different approaches to solving a BDD model have been implemented for exact computation of prime implicants. These approaches have previously been applied in static failure tree analysis. In this work the ideas for prime implicant calculation are adapted to a dynamic reliability approach combined with the multi-valued logic of DFM. In this paper the basic concepts and algorithms of YADRAT and the identified strengths and limitations of the employed approach are discussed. Also a case study illustrating the usage of YADRAT and a comparison of computational effort between two BDD implementations is presented.