13. A system comprising: at least one processor; and program code configured to be executed by the at least one processor to cause the at least one processor to: maintain a plurality of pre-computed priced travel recommendations, each pre-computed priced travel recommendation having been previously computed based on underlying data obtained from a primary data source at a time that the pre-computed priced travel recommendation was computed; associate each pre-computed priced travel recommendation with a corresponding confidence factor that indicates a probability that the associated pre-computed priced travel recommendation is still valid, the pre-computed priced travel recommendation being valid if the underlying data in the primary data source has not changed in a time period passed since the time that the pre-computed priced travel recommendation was computed and being invalid if the underlying data in the primary data source has changed in the time period; receive a travel query from a client indicating at least one travel search criterion; identify, from the plurality of pre-computed priced travel recommendations, a set of pre-computed priced travel recommendations that comply with the at least one travel search criterion; evaluate the confidence factors associated with the identified set of pre-computed priced travel recommendations; validate the pre-computed priced travel recommendations for which the confidence factor is greater than a given threshold by querying the primary data source for valid database query results; and return to the client the set of pre-computed priced travel recommendations and the validated priced travel recommendations associated with confidence factors greater than the given threshold in a response to the travel query, wherein the probability the underlying data used to compute a respective pre-computed priced travel recommendation has changed increases as a function of a duration of the time period, and the response to the travel query is returned by sending a first message conveying the set of pre-computed priced travel recommendations and a second message conveying the validated priced travel recommendations associated with confidence factors greater than the given threshold.
18. The system of claim 13 wherein the program code is configured to be executed by the at least one processor to cause the at least one processor to: derive confidence factor values from a probabilistic model that models a validity of pre-computed priced travel recommendations over time.