13. The system of claim 12 , wherein the operations comprise: classifying the query; and using the classification to select the group of candidate scoring functions from a plurality of available scoring functions.
12. A system comprising: one or more processors; and one or more memory devices configured to cause the one or more processors to perform operations comprising: receiving a query; selecting a first candidate scoring function and a second candidate scoring function from a group of at least three candidate scoring functions; presenting search results, which are responsive to the query, ordered according to scores from the first candidate scoring function; presenting the search results, which are responsive to the query, ordered according to scores from the second candidate scoring function; receiving user input selecting one of the first and second candidate scoring functions over the other; and using the user input to inform future selections of pairs of candidate scoring functions from the group of candidate scoring functions.