17. A non-transitory computer-readable storage device storing instructions that, when executed by data processing apparatus, cause the data processing apparatus to perform operations comprising: receiving a query submitted by a user to a search engine, wherein the query includes a first compound term; and in response to receiving the query, performing the following operations: generating one or more splits of the first compound term, wherein each split divides the compound term into two or more subterms, wherein at least one subterm is a term in a dictionary that associates terms with scores derived from a respective frequency of use of the subterm; assigning a score to one or more subterms of each split that are in the dictionary, wherein the score for a subterm is the score stored in the dictionary for the subterm; determining an overall score for each split from the scores for the subterms of the split; selecting one or more of the one or more splits according to the overall score for each split; and augmenting the query with the subterms of each selected split.
20. The non-transitory computer-readable storage device of claim 17 , wherein generating one or more splits of the first compound term comprises incrementally analyzing prefixes of increasing length of the first compound term to identify subterms of the prefix that appear in the dictionary.