Parse tree

From Wikipedia, the free encyclopedia

A parse tree or concrete syntax tree is a tree that represents the syntactic structure of a string according to some formal grammar. A program that produces such trees is called a parser. Parse trees may be generated for sentences in natural languages (see natural language processing), as well as during processing of computer languages, such as programming languages.

[edit] Basic description

A parse tree is made up of nodes and branches. The picture below is a linguistic parse tree representing an English sentence. In the picture, the parse tree is the entire structure, starting from S and ending in each of the leaf nodes (John,ball,the,hit).

A simple parse tree

In a parse tree, each node is either a root node, a branch node, or a leaf node. In the above example, S is a root node, NP and VP are branch nodes, while John, ball, the, and hit are all leaf nodes.

Nodes can also be referred to as parent nodes and child nodes. A parent node is one which 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 which has at least one node directly above it to which it is linked by a branch of the tree. Again from our example, hit is a child node of V.