11. The storage medium of claim 10 , wherein gathering switching data from previous queries comprises: identifying possible query phrases from the previous queries; and generating probabilities of switching between query phrases based on patterns observed in the previous queries; wherein the switching probabilities are used to determine whether a switched query phrase will be considered as a candidate synonym for a query phrase.
11. The storage medium of claim 10 , wherein gathering switching data from previous queries comprises: identifying possible query phrases from the previous queries; and generating probabilities of switching between query phrases based on patterns observed in the previous queries; wherein the switching probabilities are used to determine whether a switched query phrase will be considered as a candidate synonym for a query phrase. 14. The storage medium of claim 11 , wherein gathering switching data facilitates determining error-correction rules for queries; and wherein determining error-correction rules facilitates identifying valid synonyms for a query phrase.