For the particular case of our transition constituency parser, we use only four span features to
determine a structural action, and three to determine
a label action, in each case partitioning the sentence
exactly. The reason for this is straightforward: when
considering a structural action, the top two spans on
the stack must be considered to determine whether
they should be combined, while for a label action,
only the top span on the stack is important, since that
is the candidate for labeling. In both cases the remaining sentence prefix and suffix are also included.
These features are shown in Table 1.