1. An information retrieval system, comprising: a knowledge model database configured to store a knowledge model for a knowledge domain, the knowledge model defining a plurality of entities and interrelationships between one or more of the plurality of entities, the plurality of entities including concepts and instances; a knowledge base identifying a plurality of items including at least one question and at least one answer to the at least one question, each of the plurality of items being associated with at least one annotation identifying at least one of the entities in the knowledge model, the at least one annotation comprising a first triple statement; and a query processing server configured to: receive, from a client computer using a computer network, a natural language query, analyze the natural language query to identify a plurality of terms and interpret the natural language query as a question, determine a relationship between a pair of terms in the plurality of terms using the knowledge model, construct a second triple statement using the relationship between the pair of terms, execute a query against the knowledge base using the second triple statement to identify, within the knowledge base, a match with the first triple statement in the at least one annotation, in order to generate a set of results listing the at least one question and the at least one answer, and transmit, to the client computer, the set of results.