15. A system comprising: one or more processors; storage media storing executable instructions that, when executed by the one or more processors, cause the one or more processors to perform acts comprising: obtaining a plurality of search results for a query based on first relevance scores; classifying the plurality of search results into a plurality of classifications; generating second relevance scores for the plurality of search results based on respective rankings of the plurality of search results in corresponding classifications of the plurality of classifications; and ranking the plurality of search results based on the first relevance scores and the second relevance scores.
15. A system comprising: one or more processors; storage media storing executable instructions that, when executed by the one or more processors, cause the one or more processors to perform acts comprising: obtaining a plurality of search results for a query based on first relevance scores; classifying the plurality of search results into a plurality of classifications; generating second relevance scores for the plurality of search results based on respective rankings of the plurality of search results in corresponding classifications of the plurality of classifications; and ranking the plurality of search results based on the first relevance scores and the second relevance scores. 16. The system of claim 15 , the acts further comprising extracting a preset number of search results from the plurality of search results.