13. One or more computer-readable storage media having computer-executable instructions embodied thereon that, when executed by at least one processor, cause the at least one processor to perform acts comprising: scoring a plurality of alteration candidates for a query, the query comprising multiple query terms and each of the alteration candidates comprising multiple alteration terms, the scoring comprising, for each of the alteration candidates, performing the following: computing one or more intra-candidate dependent feature scores based on dependencies between each term of the candidate and each other term of the candidate, the computation of the one or more intra-candidate dependent feature scores being based on one or more word count models; computing one or more query-dependent feature scores based on dependencies between each alteration term and the query overall, the computation of the one or more query-dependent feature scores being based on one or more translation models; and computing a candidate score for the candidate using the feature scores; determining for each of the candidates whether to select the candidate to expand the query, the determination for each candidate using a corresponding candidate score; and for each candidate selected to expand the query, using the selected candidate to expand the query.
13. One or more computer-readable storage media having computer-executable instructions embodied thereon that, when executed by at least one processor, cause the at least one processor to perform acts comprising: scoring a plurality of alteration candidates for a query, the query comprising multiple query terms and each of the alteration candidates comprising multiple alteration terms, the scoring comprising, for each of the alteration candidates, performing the following: computing one or more intra-candidate dependent feature scores based on dependencies between each term of the candidate and each other term of the candidate, the computation of the one or more intra-candidate dependent feature scores being based on one or more word count models; computing one or more query-dependent feature scores based on dependencies between each alteration term and the query overall, the computation of the one or more query-dependent feature scores being based on one or more translation models; and computing a candidate score for the candidate using the feature scores; determining for each of the candidates whether to select the candidate to expand the query, the determination for each candidate using a corresponding candidate score; and for each candidate selected to expand the query, using the selected candidate to expand the query. 18. The one or more computer-readable storage media of claim 13 , wherein the candidate score computation for each candidate comprises computing one or more unigram feature scores based on the alteration terms.