Abstract: Large Test Collection Experiments on an Operational, Interactive System: Okapi at TREC
The Okapi system has been used in a series of experiments on the TREC
collections, investigating probabilistic models, relevance feedback and
query expansion, and interaction issues. Some new probabilistic models have
been developed, resulting in simple weighting functions which take account
of document length and within-document frequency and within query term
frequency. All have been shown to be beneficial. Relevance feedback and
query expansion are highly beneficial when based on large quantities of relevance data (as in the routing task). Interaction issues are much more
difficult to evaluate in the TREC framework and no benefits have yet been
demonstrated from feedback based on small numbers of "relevant" items
identified by intermediary searchers.