1. A method executed by a search engine for ranking items responsive to receipt of a query, the method comprising: at the search engine, responsive to receiving the query that is to be executed over a plurality of items in a data repository, identifying a document-query feature that pertains to a combination of the query and an item in the plurality of items, wherein the document-query feature is based upon: a document category that has been previously assigned to the item; and a query category that has been previously assigned to the query, wherein the query category is dependent upon document categories assigned to items previously retrieved by the search engine when executing the query over a data repository, the document-query feature is indicative of a correlation between the document category and the query category; at the search engine, retrieving items from the data repository based upon the query; ranking the items based upon document-query features assigned to the items; and responsive to ranking the items, outputting a ranked list of items, the item positioned in the ranked list of items based upon the document-query feature.
3. The method of claim 1 , further comprising assigning the query category to the query, wherein assigning the query category to the query comprises: identifying document categories assigned, respectively, to a top threshold number of items in the previously retrieved items; and assigning the query category to the query based upon the document categories that are assigned, respectively, to the top threshold number of items in the previously retrieved items.