1. A method of retrieving documents in response to a search query, the method comprising: selecting a plurality of documents that are relevant to the query by determining a relevance score for each document; determining for each document a date range for which the document associated, the date range associated with relevance data for the document during the date range; weighting the relevance score of each document according to a difference between a current date and the date range associated with the document; and ranking the selected documents according to their weighted relevance scores.