1. A method performed in a system comprising navigable nodes, documents attached to the navigable nodes, keywords associated with the navigable nodes and having search and navigation capability, the method comprising, at a node within the system: receiving an input from a user; determining that the input contains an unknown word; presenting at least one response to the user based upon the documents attached to a current node resulting from a navigation; and following presentation of the at least one response, learning one or more keyword associations for the unknown word, from the documents attached to the current node, based upon at least one additional input from the user.