The maximum entropy approach and probabilistic IR models

Abstract

This paper takes a fresh look at modeling approaches to information retrieval that have been the basis of much of the probabilistically motivated IR research over the last 20 years. We shall adopt a subjectivist Bayesian view of probabilities and argue that classical work on probabilistic retrieval is best understood from this perspective. The main focus of the paper will be the ranking formulas corresponding to the Binary Independence Model (BIM), presented originally by Roberston and Sparck Jones [1977] and the Combination Match Model (CMM), developed shortly thereafter by Croft and Harper [1979]. We will show how these same ranking formulas can result from a probabilistic methodology commonly known as Maximum Entropy (MAXENT).