CSCI 587 - Lecture 8 Grammars and Parsing

• Prolog Introduction
  • Programming using predicate logic clauses
  • Adding facts to the DataBase (assert)
  • Goals:
  • Rules: john likes anyone that likes sports and pizza
  • Family example
  • Recursive rules: ancestor
  • Lists in prolog: Notation [ F | R ]
  • Trees in list notation
    • Lisp (a ((b c) (d e) f))
    • Prolog [a ,[[b, c], [d, e], f]
• Grammars
  • Context Free Grammars(CFGs)
  • Formal definition
    • G = (N, T, P, S)
    • Derivations
    • L(G) - the language generated by G
  • Parse Trees
  • Lexical symbols
  • The Sentence Generation problem
  • Parsing
• Good Grammars
  • generality - the range of sentences analyzed correctly
  • selectivity - the range of sentences analyzed as wrong
  • understandability
• Parsing
  • Top Down Parsing
  • Bottom up Parsing
• Top Down Parsing Algorithm
  1. Initialize the Possible State List to contain ((S) 1)
  2. Then Repeat the following steps
  3. Set C = first state on the List
  4. If C = (() end of sentence) then the algorithm succeeds
  5. Else generate next states by
     • Matching a lexical symbol with the next word of the sentence
     • Applying each applicable rule and add to the possibilities list
• The Algorithm Fails by ...
• Tracing Top Down Parses
• The Chomsky Hierarchy Box 3.1
  • regular grammars
  • context sensitive
  • unrestricted
  Readings
  Sections 3.1 - 3.3
  Prolog examples in /class/csci587/Prolog : family, nlp, nlp2

  URL = http://sourgum.cs.sc.edu/~matthews/Courses/587/Lectures/lecture8.html