Cross-language Projection of Dependency Trees with Constrained Partial Parsing for Tree-to-Tree Machine Translation

Tree-to-tree machine translation (MT) that utilizes syntactic parse trees on both source and target sides suffers from the non-isomorphism of the parse trees due to parsing errors and the difference of annotation criterion between the two languages. In this paper, we present a method that projects dependency parse trees from the language side that has a high quality parser, to the side that has a low quality parser, to improve the isomorphism of the parse trees. We first project a part of the dependencies with high confidence to make a partial parse tree, and then complement the remaining dependencies with partial parsing constrained by the already projected dependencies. MT experiments verify the effectiveness of our proposed method.