For conducting abstraction based on syntactic structures, we merge a span governed by a dependency head as a node and represent it by a non-terminal in a parent node.
the i-th node N i consists of a sequence of lexical words w and non-terminals L that replace spans governed by heads in the corresponding child nodes: The edge E ij between a parent node N i and its child node N j corresponds to a governordependent relationship from the head in N i to its dependent w x in N j .