User-Chosen Phrases in Interactive Query Formulation for Information Retrieval

The impact of using phrases as content representation for documents and for queries has generally been accepted as a desirable feature in information retrieval systems because phrases are generally regarded as being more content-bearing than their constituent words. This has been borne by experiments in which the impact of phrases on retrieval performance has usually been found to be positive. However, most of the experimental results reported have derived phrases from documents and from queries in a fully automatic way. While this is acceptable for document indexing it is less acceptable for query formulation which is increasingly heading towards being an iterative process with users investing time in browsing the term space to choose appropriate search terms. In this paper we report a series of experiments in which two users, one experienced and the other a novice, formulate their queries by browsing the term space in advance of issuing a retrieval request. For these users we analyse the relative contributions and the impact of single words and multi-word phrases as search terms, on overall retrieval performance. Our results have implications for how choosing phrases as search terms should be presented to novice and to experienced searchers.