1. A tree ordering component within a sentence realization system which receives an unordered syntax tree and generates a scored and ranked list of alternative ordered syntax trees from the unordered syntax tree, the tree ordering component comprising: a statistical model of constituent structure conditioned on features, having a formal structure, and whose parameters are estimated using a statistical estimation technique; and a search component which receives the unordered syntax tree, considers the set of possible alternative ordered syntax trees, and identifies which of the alternative ordered syntax trees has a highest probability according to the statistical model of constituent structure.