Outline of a General Probabilistic Retrieval Model

For reasons of technical convenience, current retrieval algorithms based on probabilistic reasoning are derived from models that assume patrons evaluate documents using a two value relevance scale. This paper extends the theory by describing a model which includes a more general relevance scale. This model permits a re‐examination of the earlier theory as a special case of that developed here and leads to a more satisfying interpretation of the ranking principle of the earlier models.