15. The computing system of claim 13 , wherein the first information source comprises a knowledge base including structured data having a format compatible with the one or more queries, and wherein the one or more alternate information sources include a user by whom the input was entered.
15. The computing system of claim 13 , wherein the first information source comprises a knowledge base including structured data having a format compatible with the one or more queries, and wherein the one or more alternate information sources include a user by whom the input was entered. 17. The computing system of claim 15 , wherein the one or more variables of the one or more queries include the first variable and a second variable, and wherein the one or more computing devices are configured to determine whether the unknown information represented by the second variable can be retrieved from one or more alternate information sources by referring to contextual information.