At the heart of the Okapi system is a formula referring to some half a dozen variables, which estimate the probability that a given document is relevant to a given query. User interface design for Okapi aims to present its search capabilities as clearly and simply as possible. But between the...

A brief review of the history of laboratory testing of information retrieval systems focuses on the idea of a general‐purpose test collection of documents, queries and relevance judgements. The TREC programme is introduced in this context, and an overview is given of the methods used in TREC....