8. A computing system, comprising: one or more data stores in a computing network, the one or more data stores having a knowledge base stored therein including a plurality of entity objects and a plurality of facts, each fact corresponding to at least one of a plurality of fact types; and one or more computing device in the computing network configured to: identify first relation data in the knowledge base corresponding to a plurality of facts of a first fact type, wherein for each fact of the first fact type in the knowledge base the first relation data express a relationship for a pair of the entity objects, and wherein for each fact of the first fact type in the knowledge base the first relation data require that one of the pair of entity objects has a unique value for a given value of the other of the pair of entity objects; identify an entity object class based on which of the pair of entity objects corresponding to a first fact of the first fact type is unique; identify a first subset of the entity objects that correspond to the entity object class and for which corresponding facts of the first fact type are not represented in the knowledge base; responsive to identification of the first subset of entity objects, select a first entity object from the first subset of entity objects for generation of a new fact of the first fact type; generate a search engine query using the first relation data and the first entity object; search a set of documents using the search engine query to generate search results; parse the search results to identify first information representing the first relation data for the entity corresponding to the first entity object; generate the new fact for addition to the knowledge base using the first information, the first entity object, and the first relation data; add the new fact to the knowledge base; and repeat the selecting, generating, searching, parsing, generating, and adding for each of the entity objects included in the first subset of the entity objects.
9. The computing system of claim 8 , wherein the one or more computing devices are configured to identify the first relation data by: receiving natural language input from a user; generating a knowledge base query for use with the knowledge base using the natural language input, the knowledge base query identifying the first entity object and the first relation data; and determining that a fact corresponding to the first relation data is not expressed in the knowledge base for the first entity object by processing the knowledge base query with reference to the knowledge base.