document: Online expansion of rare queries for sponsored search 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 can not be applied in real-time . In practice , such algorithms are applied offline 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 offline . The approach builds an expanded query representation by leveraging offline processing done for related popular queries . Our experimental results show that our approach significantly improves the effectiveness of advertising on rare queries with only a negligible increase in computational cost .
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