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Linguistics

Notes This parse tree is simplified; for more information, see X-bar theory. The parse tree is the entire
structure, starting from S and ending in each of the leaf nodes (John, hit, the, ball). The following
abbreviations are used in the tree:
1. S for sentence, the top-level structure in this example

2. NP for noun phrase. The first (leftmost) NP, a single noun "John", serves as the subject of the
sentence. The second one is the object of the sentence.
3. VP for verb phrase, which serves as the predicate
4. V for verb. In this case, it's a transitive verb hit.
5. D for determiner, in this instance the definite article "the"
6. N for noun

Each node in the tree is either a root node, a branch node, or a leaf node. S is the root node, NP and
VP are branch nodes, and John, hit, the, and ball are all leaf nodes. The leaves are the lexical
tokens of the sentence.[2] A node can also be referred to as parent node or a child node. A parent
node is one that has at least one other node linked by a branch under it. In the example, S is a
parent of both NP and VP. A child node is one that has at least one node directly above it to which
it is linked by a branch of the tree. From the example, hit is a child node of V. The terms mother
and daughter are also sometimes used for this relationship.

25.5 Dependency-Based Parse Trees
The dependency-based parse trees of dependency grammars[3] 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:

V

N
D Dependency-based parse tree

John hit the ball

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.

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