Query Expansion

Query expansion involves taking documents judged relevant by the user as the basis for a new search to find others which are "similar". Words and phrases are extracted from the relevant documents, weighted, and added to the existing search terms to generate an expanded query. Early evaluation of this facility (see Okapi '88) showed that it was effective for finding documents on the same topics as those already chosen.

Recent Okapi studies have examined the way in which users cope with this facility, and how the interface should be designed to present the concept of query expansion. It can operate in two different ways:

The methods were compared in the Okapi '94 experiments. Results suggested that giving users more control over the inclusion of new words and phrases in an expanded search was not always beneficial. Few subjects took up IQE, and those who did tended to be highly selective, making the expansion facility less effective.

A later research project, Enquire Okapi, re-examined query expansion methods, and investigated how best to combine AQE and IQE with thesaurus searching, so as to gain maximum benefit from user relevance judgements in improving search performance. The new interface introduced the concept of dynamic or incremental query expansion.