1. A named-entity recognition system comprising: a multilevel hidden Markov model, said hidden Markov model including: (a) at least one upper level representing named entities; and (b) at least one lower level representing words generated by the upper level.
5. A named-entity recognition system according to claim 1, wherein at least one of the transitions between said upper levels is conditioned on the output of the previous lower states, and at least one of the transitions between the lower states is conditioned on the output of the previous upper state.