1. A knowledge representation system, comprising: a data store having a knowledge base stored therein comprising first knowledge represented in a structured, machine-readable format which encodes meaning; and at least one computing device operable to: add second knowledge to the knowledge base, the second knowledge being generated with reference to input from a plurality of users which is not in the structured, machine-readable format, at least some of the input from the users being in a natural language; generate third knowledge not represented in the knowledge base by inferring the third knowledge from at least one of the first knowledge and the second knowledge; and respond to queries using at least one of the first knowledge, the second knowledge, and the third knowledge.