Okapi at TREC-5

City submitted two runs each for the automatic ad hoc, very large collection track, automatic routing and Chinese track; and took part in the interactive and ltering tracks. There were no very signi cant new developments; the same Okapi-style weighting as in TREC{3 and TREC{4 was used this time round, although there were attempts, in the ad hoc and more notably in the Chinese experiments, to extend the weighting to cover searches containing both words and phrases. All submitted runs except for the Chinese incorporated run-time passage determination and searching. The Okapi back-end search engine has been considerably speeded, and a few new functions incorporated. See Section 3.