HUGIN - A Shell for Building Bayesian Belief Universes for Expert Systems

Abstract

Causal probabilistic networks have proved to be a useful knowledge representation tool for modelling domains where causal relations- in a broad sense- are a natural way of relating domain objects and where uncertainty is inherited in these relations. This paper outlines an implementationthe HUG IN shell-for handling a domain model expressed by a causal probabilistic network. The only topological restriction imposed on the network is that it must not contain any directed loops. The approach is illustrated step by step by solving a genetic breeding problem. A graph representation of the domain model is interactively created by using instances of the basic network componentsnodes and arcs-as building blocks. This structure, together with the quantitative relations between nodes and their immediate causes expressed as conditional probabilities, are automatically transformed into a tree structure, a junction tree. Here a computationally efficient and conceptually simple algebra of Bayesian belief universes supports incorporation of new evidence, propagation of information, and calculation of revised beliefs in the states of the nodes in the network. Finally, as an example of a real world application, MUNIN- an expert system for electromyography- is discussed.