30. The system of claim 28 , wherein if a switching probability is above a specified threshold, the switched phrase will be considered a candidate synonym.
28. The system of claim 27 , 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.