document: Generating query substitutions We introduce the notion of query substitution , that is , generating a new query to replace a user 's original search query . Our technique uses modifications based on typical substitutions web searchers make to their queries . In this way the new query is strongly related to the original query , containing terms closely related to all of the original terms . This contrasts with query expansion through pseudo-relevance feedback , which is costly and can lead to query drift . This also contrasts with query relaxation through boolean or TFIDF retrieval , which reduces the specificity of the query . We define a scale for evaluating query substitution , and show that our method performs well at generating new queries related to the original queries . We build a model for selecting between candidates , by using a number of features relating the query-candidate pair , and by fitting the model to human judgments of relevance of query suggestions . This further improves the quality of the candidates generated . Experiments show that our techniques significantly increase coverage and effectiveness in the setting of sponsored search .
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