To extract dependency relations from these parse trees, we scan for attachment rules (e.g., L 1 H → Y A L ′ H ) and record that A depends on H. The schema omits the rules for right arguments since they are symmetric.
the posterior P (θ|s, t, α) is also a product of Dirichlets, also factoring into a Dirichlet for each nonterminalN , where the parameters αr are augmented by the number of times rulē r is observed in tree t: We can see that αr acts as a pseudocount of the number of timesr is observed prior to t. To make use of this prior, we use the Variational Bayes (VB) technique for PCFGs with Dirichlet Priors presented by Kurihara and Sato (2004).