: The explosion of data stored in commercial or administrational databases calls for intelligent techniques to discover the patterns hidden in them and thus to exploit all available information. Therefore a new line of research has recently been established, which became known under the names "Data Mining " and "Knowledge Discovery in Databases". In this paper we study a popular technique from its arsenal of methods to do dependency analysis, namely learning inference networks (also called "graphical models") from data. We review the already well-known probabilistic networks and provide an introduction to the recently developed and closely related possibilistic networks. The latter can be expected to have some impact on industrial applications, because they are especially suited to handle not only uncertain, but also imprecise information. 1 Introduction Due to the advances in hardware and software technology, large databases (product databases, customer databases, etc.) are nowadays ..