So, the general probability can be simplified to: where h k is a lexical word, h k+1 is the head word of h k , and o k ∈ {⟨L⟩, ⟨R⟩} is retained in the history to show the dependency orientation.
we further propose an expectation-maximization (EM) algorithm for estimating the probability of arbitrary order 3 dependency N-grams, by considering all possible dependency structures 4 of a sentence (Fig.