Natural Language Understanding Wiki

Spurious ambiguity is a problem in transition-based dependency parsing using static oracle in which there is more than one sequence of transitions leading to a gold parse. According to Goldberg et al. (2012):

Most transition systems, including the arc-eager and arc-standard systems described in Nivre (2003, 2004), exhibit spurious ambiguity and map several sequences to the same gold tree.

Arc-standard transition system[]

Ambiguity when a head node links to its left and right side (a <- b -> c). There are two sequences leading to this tree structure:

  1. S S TODO
  2. S S ...

Arc-eager transition system[]

Shift-reduce ambiguity: <Shift Left-arc Reduce> and <Reduce Shift Left-arc> lead to the same tree