Abstract: Okapi at TREC

The Okapi retrieval system is described technically and in terms of its design principles. These include simplicity, robustness and ease of use. The version of Okapi used for TREC is further discussed. Designing experiments within the TREC constraints but using Okapi's supposed strengths proved problematic and some compromise was necessary. The official TREC runs were (a) very simple automatic processing of the ad-hoc topics; (b) manually constructed ad-hoc queries; (c) feedback on the manual queries from searchers' relevance judgements; and (d) routing queries automatically obtained using the training set in a form of relevance feedback. The best run (manual with feedback), although not up to the best reported TREC results, was respectable, and an encouragement to further development within the same principles.