TY - CONF ID - www200952 UR - http://www2009.eprints.org/52/ A1 - Broder, Andrei A1 - Ciccolo, Peter A1 - Gabrilovich, Evgeniy A1 - Josifovski, Vanja A1 - Metzler, Donald A1 - Riedel, Lance A1 - Yuan, Jeffrey Y1 - 2009/04// N2 - Sponsored search systems are tasked with matching queries to relevant advertisements. The current state-of-the-art matching algorithms expand the user?s query using a variety of external resources, such as Web search results. While these expansion-based algorithms are highly effective, they are largely inefficient and cannot be applied in real-time. In practice, such algorithms are applied o?ine to popular queries, with the results of the expensive operations cached for fast access at query time. In this paper, we describe an efficient and effective approach for matching ads against rare queries that were not processed o?ine. The approach builds an expanded query representation by leveraging o?ine processing done for related popular queries. Our experimental results show that our approach signi?cantly improves the effectiveness of advertising on rare queries with only a negligible increase in computational cost. TI - Online Expansion of Rare Queries for Sponsored Search SP - 511 M2 - Madrid, Spain AV - public EP - 511 T2 - 18th International World Wide Web Conference ER -