15. A computer-readable storage device storing computer-executable instructions that, when executed by one or more computer systems, configure the one or more computer systems to perform operations comprising: presenting an interface for a search engine; receiving a search string from a user; searching a first data set using a first search index based at least in part on a search query that includes the search string; obtaining first search results including a subset of the first data set based at least in part on said searching the first data set using the first search index; identifying a second search index from among a plurality of predetermined indices based at least in part on the first search results; searching the first search results using the second search index; obtaining second search results from among the subset of the first data set based at least in part on the second search index; ranking at least a part of the second search results with respect to each other based at least in part on a ranking algorithm of the second search index; modifying the second search index based at least in part on the ranked part of the second search results and data that is obtained independent of the second search results; and transmitting the second search results to the user.
17. The computer-readable storage device of claim 15 , further comprising instructions for modifying the plurality of predetermined indices based on seasonal information.