Parse Tree - Dependency-based Parse Trees

Dependency-based Parse Trees

The dependency-based parse trees of dependency grammars see all nodes as terminal, which means they do not acknowledge the distinction between terminal and non-terminal categories. They are simpler on average than constituency-based parse trees because they contain many fewer nodes. The dependency-based parse tree for the example sentence above is as follows:

This parse tree lacks the phrasal categories (S, VP, and NP) seen in the constituency-based counterpart above. Like the constituency-based tree however, constituent structure is acknowledged. Any complete subtree of the tree is a constituent. Thus this dependency-based parse tree acknowledges the subject noun John and the object noun phrase the ball as constituents just like the constituency-based parse tree does.

The constituency vs. dependency distinction is far-reaching. Whether the additional syntactic structure associated with constituency-based parse trees is necessary or beneficial is a matter of debate.