说明：  Creating Search history Any personal documents such as browsing history and emails on a user’s computer could be the data source for user profiles. This focus on frequent terms limits the dimensionality of the document set, which further provides a clear description of users’ interest. This module allows the search engine to better understand a user’s session and potentially tailor that user’s search experience according to the needs. Once query groups, which have been identified, that the search engines can have a very good representation of the search context behind the current query using queries and clicks in the corresponding query group.