Page 329 - DENG504_LINGUISTICS

Unit 25: Transformational Rules: Application-Tree Diagrams

P : preposition Notes
C : conjunction
When working with trees, linguists write systems of rules (called 'grammars') which
describe sets of trees. Each rule in the system is a building block. Any tree which can be constructed
out of those building blocks is in the set of trees described by the grammar. For example, the tree
given above for These dogs chased those cats. requires the following building blocks or rules:
S NP VP

NP VP D N V NP

D D N N V

these those dogs cats chased
Sometimes, sentences have multiple meanings, and these meanings can be described in
terms of different groupings of words, or different trees. For example, the sentence The
tourist saw the astronomer with the telescope. could mean either of the following things:
1. The tourist used the telescope to see the astronomer.
2. The astronomer that the tourist saw had a telescope.
The difference is whether the prepositional phrase (PP) with the telescope is grouped with
saw the astronomer or just the astonomer. We can use tree diagrams to show this difference.
A concrete syntax tree or parse tree or parsing tree is an ordered, rooted tree that represents the
syntactic structure of a string according to some formal grammar. Parse trees are usually constructed
according to one of two competing relations, either in terms of the constituency relation of
constituency grammars (= phrase structure grammars) or in terms of the dependency relation of
dependency grammars. Parse trees are distinct from abstract syntax trees (also known simply as
syntax trees), in that their structure and elements more concretely reflect the syntax of the input
language. 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.
25.4 Constituency-Based Parse Trees

The constituency-based parse trees of constituency grammars (= phrase structure grammars)
distinguish between terminal and non-terminal nodes. The interior nodes are labeled by non-
terminal categories of the grammar, while the leaf nodes are labeled by terminal categories. The
image below represents a constituency-based parse tree; it shows the syntactic structure of the
English sentence John hit the ball:
S

N
VP

Constituency-based parse tree
V NP

D N

John hit the ball

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