12. A system that facilitates ranking items returned by a search engine in response to receipt of a query, the system comprising: a processor; and a memory that comprises a plurality of components that are executed by the processor, the plurality of components comprising: a receiver component that receives a document category previously assigned to a first item and a query category previously assigned to the query; a computation component that computes a document-query feature for a combination of the first item and the query, the document-query feature computed based upon the document category and the query category, the document-query feature indicative of whether the document category matches the query category, the query category previously assigned to the query based upon document categories assigned to items previously retrieved by the search engine based upon the query; and a ranker component that receives the items returned by the search engine and outputs a ranked list of items based upon the query, a position of the first item in the ranked list of items based upon the document-query feature.
12. A system that facilitates ranking items returned by a search engine in response to receipt of a query, the system comprising: a processor; and a memory that comprises a plurality of components that are executed by the processor, the plurality of components comprising: a receiver component that receives a document category previously assigned to a first item and a query category previously assigned to the query; a computation component that computes a document-query feature for a combination of the first item and the query, the document-query feature computed based upon the document category and the query category, the document-query feature indicative of whether the document category matches the query category, the query category previously assigned to the query based upon document categories assigned to items previously retrieved by the search engine based upon the query; and a ranker component that receives the items returned by the search engine and outputs a ranked list of items based upon the query, a position of the first item in the ranked list of items based upon the document-query feature. 16. The system of claim 12 , the ranked list of items comprises a second item that is assigned a second document category, a second document-query feature for the second item is based upon a score assigned to the second category that is assigned to the second item, the ranker component ranks the item relative to the second item as a function of a value of the document-query feature relative to the score.