Directed cycles in bayesian belief networks: probabilistic semantics and consistency checking complexity

  • Authors:
  • Alexander L. Tulupyev;Sergey I. Nikolenko

  • Affiliations:
  • St.Petersburg Institute for Informatics and Automation of the Russian Academy of Sciences;St.Petersburg Institute for Informatics and Automation of the Russian Academy of Sciences

  • Venue:
  • MICAI'05 Proceedings of the 4th Mexican international conference on Advances in Artificial Intelligence
  • Year:
  • 2005

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Abstract

Although undirected cycles in directed graphs of Bayesian belief networks have been thoroughly studied, little attention has so far been given to a systematic analysis of directed (feedback) cycles. In this paper we propose a way of looking at those cycles; namely, we suggest that a feedback cycle represents a family of probabilistic distributions rather than a single distribution (as a regular Bayesian belief network does). A non-empty family of distributions can be explicitly represented by an ideal of conjunctions with interval estimates on the probabilities of its elements. This ideal can serve as a probabilistic model of an expert's uncertain knowledge pattern; such models are studied in the theory of algebraic Bayesian networks. The family of probabilistic distributions may also be empty; in this case, the probabilistic assignment over cycle nodes is inconsistent. We propose a simple way of explicating the probabilistic relationships an isolated directed cycle contains, give an algorithm (based on linear programming) of its consistency checking, and establish a lower bound of the complexity of this checking.