Is the First Query the Most Important: An Evaluation of Query Aggregation Schemes in Session Search

Web users often issue a series of related queries, which form a search session, to fulfill complicated information needs. Query aggregation utilizes and combines multiple queries for session search. Prior research has demonstrated that query aggregation is an effective technique for session search that can generally achieve a 15% ∼ 20% nDCG@10 improvement on finding relevant documents for the last query. When aggregating queries in a session, how to put weights on them for the most effective search is an interesting question. Is the first query or the last query plays a more important role and thus deserves a higher weight in the session? This paper evaluates various query aggregation schemes and proposes a new three-step query aggregation method. Evaluation on TREC 2011 and TREC 2012 Session Tracks shows that the proposed scheme works very well and significantly outperforms the best TREC systems.