17. A system, comprising: a data store having a knowledge base stored therein comprising first knowledge represented in a structured, machine-readable format, the data store also having a plurality of generators stored therein, each generator including a fact pattern representing one or more characteristics of facts that can be generated by that generator, and code for generating the facts; and one or more computing devices configured to: generate second knowledge for inclusion in the knowledge base by inferring the second knowledge from the first knowledge using a first generator of the plurality of generators; determine that the second knowledge is not semantically contradicted by other knowledge in the knowledge base; store the second knowledge in the knowledge base in association with related knowledge information identifying the first knowledge from which the second knowledge was inferred; generate a first query, a second query, and a third query, including translating one or more corresponding natural language questions; respond to the first query using the first knowledge; respond to the second query using the second knowledge; identify a second generator of the plurality of generators for which the included fact pattern is compatible with the third query; dynamically generate third knowledge not represented in the knowledge base in response to the third query by inferring the third knowledge from one or both of the first knowledge and the second knowledge using the second generator; store the third knowledge in a cache; retrieve the third knowledge from the cache as part of recursive processing of the third query; respond to the third query using the third knowledge; determine that the first knowledge from which the second knowledge was inferred is no longer valid; and remove the second knowledge from the knowledge base using the related knowledge information.
22. The system of claim 17 , wherein the one or more computing devices are configured to determine that the second knowledge is not semantically contradicted by other knowledge in the knowledge base by: identifying a first fact corresponding to the second knowledge, the first fact including two entity objects and a first relation object representing a first relationship between the two entity objects; and determining that there are no facts in the knowledge base that include the two entity objects and a different relation object representing a different relationship that conflicts with the first relationship.