Dependency Grammar

Dependency Grammar

• phrasal constituents (verb phrases, noun phrases, prepositional phrases, etc) & phrase-structure rules do not play a direct role
• the syntactic structure of a sentence is described solely in terms of the words (or lemmas) in a sentence and an associated set of directed binary grammatical relations that hold among the words

Dependency Tree

A dependency tree is a directed graph that satisfies the following constraints:

• there is a single designated root node that has no incoming arcs
• with the exception of the root node, each vertex has exactly one incoming arc
• there is a unique path from the root node to each vertex in V.

Taken together, these constraints ensure that:

• each word has a single head
• that the dependency structure is connected
• that there is a single root node from which one can follow a unique directed path to each of the words in the sentence

Dependency Tree - Example

Indent

Relations among the words are illustrated in the above sentence with directed, labeled arcs from heads to dependents. We call this a typed dependency structure typed dependency because the labels are drawn from a fixed inventory of grammatical relations. It also includes a root node that explicitly marks the root of the tree, the head of the entire structure

Projectivity

an arc from a head to a dependent is said to be projective if there is a path from the head to every word that lies between the head and the dependent in the sentence.

a dependency tree is said to be projective if all the arcs that make it up are projective

Dependency Relation Sets

• Universal Dependency Project Set