14. The system of claim 13 , wherein the computer-executable instructions further cause the processing unit to: tag an individual first query entered by the user as part of the first historical search context based on a first vertical search engine to which the individual first query was submitted by the user as part of the first historical search context; and tag an individual second query entered by the user as part of the second historical search context based on a second vertical search engine to which the individual second query was submitted by the user as part of the second historical search context.
14. The system of claim 13 , wherein the computer-executable instructions further cause the processing unit to: tag an individual first query entered by the user as part of the first historical search context based on a first vertical search engine to which the individual first query was submitted by the user as part of the first historical search context; and tag an individual second query entered by the user as part of the second historical search context based on a second vertical search engine to which the individual second query was submitted by the user as part of the second historical search context. 15. The system of claim 14 , wherein the computer-executable instructions further cause the processing unit to: tag an individual current query entered by the user during the current user session based on a third vertical search engine to which the individual current query was submitted by the user.