Probabilistic Decision Graphs (PDGs) combine elements of probabilistic graphical models and ordered binary decision diagrams (OBDDs). PDGs were first proposed by M. Bozga and O. Maler in the context of probabilistic verification. We have introduced a slightly generalized version of PDGs, and investigated their properties from a reasoning under uncertainty point of view. Special focus of this work is a comparison with Bayesian networks with regard to efficiency of probabilistic inference, and with regard to the probabilistic independence models that can be represented by the graphical structures in the two frameworks. The results show that PDGs and Bayesian networks represent different kinds of independence structures: whereas independence structures encoded by Bayesian networks are given in terms of subsets of random variables, the independence structures encoded by PDGs are given in terms of partitions of the state space. For probability distributions exhibiting the latter type of independence patterns, one can obtain significantly more efficient representations (with regard to complexity of probabilistic inference) with PDGs than with Bayesian networks. We also have developed and implemented a learning algorithm for PDGs. We have conducted experiments in which both PDG and Bayesian network models were learned from real-life data sets. Goal of the experiments was to determine whether for some types of data the learning algorithms for the two frameworks would produce models with significantly different inference complexity. Somewhat surprisingly, the results showed that the learned models in the two representation languages exhibited quite similar complexity characteristics.
|Periode||19/05/10 → …|