Standard models for syntactic dependency parsing take words to be the
elementary units that enter into dependency relations. In this paper, we
investigate whether there are any benefits from enriching these models with the
more abstract notion of nucleus proposed by Tesni\`{e}re. We do this by showing
how the concept of nucleus can be defined in the framework of Universal
Dependencies and how we can use composition functions to make a
transition-based dependency parser aware of this concept. Experiments on 12
languages show that nucleus composition gives small but significant
improvements in parsing accuracy. Further analysis reveals that the improvement
mainly concerns a small number of dependency relations, including nominal
modifiers, relations of coordination, main predicates, and direct objects.Comment: Accepted at EACL-202
