CSCI 587 - Lecture 15 Parsing with Features

• Article-Noun agreement: (NP NUMBER ?n) -> (art NUMBER ?n) (n NUMBER ?n)
• A simple lexicon with features
• Abbreviated Notation for grammars with features
  • Binary features for C: (C B +) denoted C[+B]
  • If Values of a feature are unique then drop the Feature name
    _np_vp:inf is clearly a SUBCAT value so
    (VP SUBCAT _np_vp:inf) represented as (VP _np_vp:inf)
  • Head Features - Frequently features of the LHS (mother clause) are constrained to have the same value as in the head subconstituent.
    In this case just list the head features elsewhere and drop them from the grammar that is written down.
• Example: (S INV - AGR ?a VFORM ?v{pres, past}) -> (NP AGR ?a)(VP AGR ?a VFORM ?v{pres, past})
  1. Rewriting the binary feature yields S[-INV]
  2. Listing AGR and VFORM as head features for S simplifies to
     S[-INV] -> (NP AGR ?a)(VP AGR ?a VFORM ?v{pres, past})
• Simple Grammar in abreviated form
• Expanding
• The expanded grammar
• Parse trees with features
• Parsing with Features
  1. Word = a
  2. C = (ART ROOT A AGR 3s)
  3. Matches the Rule (NP AGR ?a) -> . (ART AGR ?a) (N AGR ?a)
  4. But in matching we assign variable ?a = 3s
  5. To obtain the Arc (NP AGR 3s) -> (ART AGR 3s) . (N AGR 3s)
  6. after seeing fish that extends this arc further we "reduce" and add the constituent (NP AGR 3s) to the chart
• Prolog Parse Trees as functors (nlp4)
• Features in Prolog
  • list of features
  • functor
• CUT in prolog

Readings

Sections 4.3-4.5

Assignment 5 p 78 #8, Implement the CFG in p76-77 #5 in prolog, p 79 #11 a, p 118 #1