Since the system inputs are the golden POS tags in the treebank, we use the boundary words and the boundary POS tags interchangeably in this paper.
in some parse tree T , we consider the boundary POS tags of each constituent and define the new probabilistic model as where distribution P C C G is the basic CCG model defined in section 4.1, P BDR is the proposed boundary model, σ 〈i, j〉 means the boundary words of the constituent covered by span 〈i, j〉, and B is a special nonterminal representing the constituent spans.