Natural Language Processing 5 Chomsky Hierarchy

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Natural Language Processing(5)Chomsky
Hierarchy

• Dr. Xuan Wang(? ?)
• Intelligence Computing Research Center
• Harbin Institute of Technology Shenzhen Graduate
  School
• Slides from Dr.Dekang Lin CS University of
  Alberta

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• Computation, which predates computers by
  centuries (e.g., Euclid), has two components that
  affect language processing
• 1. Engineering techniques for building machines
  and software
• 2. Theory concerned with the underlying models
  and ideas (mathematics, linguistics, biology,
  physics, etc.).
• In language processing and compiler
  construction, the theoretical study of grammars
  has been of importance. Other influences come
  from mathematics, e.g., graph theory,
  probability, algebra, linear algebra.

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Syntactic Analysis

• Computer and Natural Languages are very
  productive. They are also highly regular in
  character. Hence, any grammar which is generated
  to accept all structurally correct strings must
  account for this productivity and regularity.
• To describe the regularity and productivity of
• languages, we provide rules of syntax (or
  tructure).
• Our rules of syntax should specify the syntactic
• structure of a string in our language.

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Syntactic Analysis

• To provide a syntactic analysis for a string, we
  musthave
• A Grammar the formal specification of
  allowablestructures.
• A Parsing Algorithm a method of analyzing
  thesentence to determine its structure.

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Syntactic Analysis

• Why worry about structurally correct strings?
• It's a lot easier to do syntax-directed
  translation of a language
• Syntax is an excellent constraint on word
• recognition, OCR, etc..
• Grammar Checking

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• Generative grammars can be thought of as a set of
  rules that generate valid phrases in a particular
  language. Noam Chomsky defined four classes of
  "complexity" for generative grammars, that are
  commonly organized into the Chomsky Hierarchy.
• A key imperfection characteristics of grammars
• are not always related to the language they
  describe. It can be difficult to understand the
  relationship between structure and meaning (or
  semantics).

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The Chomsky Hierarchy
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Regular Grammars (type 3)
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Regular Expressions
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Simple Transition Networks
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Context-free Grammars (type 2)
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Recursive Transition Networks
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Methods of Showing the StructuralAnalysis of a
Sentence
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Ambiguity
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Context Sensitive Grammars(type1)
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General Grammars (type 0)
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CFGs and Determinism
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CFG Normal Forms
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Noam Chomsky

• Noam Chomsky was born on December 7, 1928 in
  Philadelphia, Pennsylvania. His undergraduate and
  graduate years were spent at the University of
  Pennsylvania where he received his PhD in
  linguistics in 1955. During the years 1951 to
  1955, Chomsky was a Junior Fellow of the Harvard
  University Society of Fellows. While a Junior
  Fellow he completed his doctoral dissertation
  entitled, "Transformational Analysis." The major
  theoretical viewpoints of the dissertation
  appeared in the monograph Syntactic Structure,
  which was published in 1957. This formed part of
  a more extensive work, The Logical Structure of
  Linguistic Theory, circulated in mimeograph in
  1955 and published in 1975.

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Chomsky on terrorism
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• Chomsky joined the staff of the Massachusetts
  Institute of Technology in 1955 and in 1961 was
  appointed full professor in the Department of
  Modern Languages and Linguistics (now the
  Department of Linguistics and Philosophy.) From
  1966 to 1976 he held the Ferrari P. Ward
  Professorship of Modern Languages and
  Linguistics. In 1976 he was appointed Institute
  Professor

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• During the years 1958 to 1959 Chomsky was in
  residence at the Institute for Advanced Study at
  Princeton, NJ. In the spring of 1969 he delivered
  the John Locke Lectures at Oxford in January
  1970 he delivered the Bertrand Russell Memorial
  Lecture at Cambridge University in 1972, the
  Nehru Memorial Lecture in New Delhi, and in 1977,
  the Huizinga Lecture in Leiden, among many others.

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Worlds Superstar2002 Turing Award Winners
Ole-Johan DahlKristen Nygaard

• For ideas fundamental to the emergence of object
  oriented programming, through their design of the
  programming languages Simula I and Simula 67.

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