Understanding Natural Language

1
Understanding Natural Language
14
14.0 The Natural Language Understanding Problem
14.1 Deconstructing Language A
Symbolic Analysis 14.2 Syntax 14.3 Syntax and
Knowledge with ATN parsers
14.4 Stochastic Tools for Language
Analysis 14.5 Natural Language Applications 14.6
Epilogue and References 14.7 Exercises
Additional source used in preparing the
slides Patrick H. Winstons AI textbook, Addison
Wesley, 1993.
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Alternative to CSGs

• Retain simple structure of CFGs
• Augment them with procedures that perform the
  necessary contextual tests
• Attach features to terminals and
  nonterminalsaugmented transition networks

3
Parsing with ATNs

• Attach procedures to the arcs of the network.
• The parser will execute those procedures while
  traversing the arcs.
• The procedures
• Perform tests
• Construct a parse tree
• Both terminals and nonterminals are represented
  as identifiers with attached features.

4
Frames for three nonterminals
Sentence
Noun phrase
Verb phrase
Verb phrase
Verb
Number
Object
Noun phrase
Determiner
Noun
Number
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Dictionary entries - 1
like
likes
PART_OF_SPEECH verb
ROOT like
NUMBER plural
PART_OF_SPEECH verb
ROOT like
NUMBER singular
bite
bites
PART_OF_SPEECH verb
ROOT bite
NUMBER plural
PART_OF_SPEECH verb
ROOT bite
NUMBER singular
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Dictionary entries - 2
men
man
PART_OF_SPEECH noun
ROOT man
NUMBER plural
PART_OF_SPEECH noun
ROOT man
NUMBER singular
dogs
dog
PART_OF_SPEECH noun
ROOT dog
NUMBER plural
PART_OF_SPEECH noun
ROOT dog
NUMBER singular
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Dictionary entries - 3
a
the
PART_OF_SPEECH article
ROOT a
NUMBER singular
PART_OF_SPEECH article
ROOT the
NUMBER plural or singular
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Sentence
noun_phrase
verb_phrase
init
final
1
2

• function sentence-1 begin NOUN_PHRASE
  structure returned by noun_phrase network
  SENTENCE.SUBJECT NOUN_PHRASE end.

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Sentence
noun_phrase
verb_phrase
init
final
1
2

• function sentence-2 begin VERB_PHRASE
  structure returned by verb_phrase network if
  NOUN_PHRASE.NUMBER VERB_PHRASE.number
  then begin SENTENCE.VERB_PHRASE
  VERB_PHRASE return SENTENCE end
  else fail end.

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Noun_phrase
article
noun
init
final
1
2
noun
3

• function noun_phrase-1 begin ARTICLE
  definition frame for next word of input if
  ARTICLE.PART_OF_SPEECH article then
  NOUN_PHRASE.DETERMINER ARTICLE
  else fail end.

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Noun_phrase
article
noun
init
final
1
2
noun
3

• function noun_phrase-2 begin NOUN
  definition frame for next word of input if
  NOUN.PART_OF_SPEECH noun and NOUN.NUMBER
  agrees with NOUN_PHRASE.DETERMINER.NUMBER
  then begin NOUN_PHRASE.NOUN
  NOUN NOUN_PHRASE.NUMBER NOUN.NUMBER
  return NOUN_PHRASE end else
  fail end.

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Noun_phrase
article
noun
init
final
1
2
noun
3

• function noun_phrase-3 begin NOUN
  definition frame for next word of input if
  NOUN.PART_OF_SPEECH noun then begin
  NOUN_PHRASE.DETERMINER unspecified
  NOUN_PHRASE.NOUN NOUN
  NOUN_PHRASE.NUMBER NOUN.NUMBER end
  else fail end.

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Verb_phrase
verb
noun_phrase
init
final
1
2
verb
3

• function verb_phrase-1 begin VERB
  definition frame for next word of input if
  VERB.PART_OF_SPEECH verb then begin
  VERB_PHRASE.VERB VERB
  VERB_PHRASE.NUMBER VERB.NUMBER
  end end.

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Verb_phrase
verb
noun_phrase
init
final
1
2
verb
3

• function verb_phrase-2 begin NOUN_PHRASE
  structure returned by noun_phrase network
  VERB.PHRASE.OBJECT NOUN_PHRASE return
  VERB_PHRASE end.

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Verb_phrase
verb
noun_phrase
init
final
1
2
verb
3

• function verb_phrase-3 begin VERB
  definition frame for next word of input if
  VERB.PART_OF_SPEECH verb then begin
  VERB_PHRASE.VERB VERB
  VERB_PHRASE.NUMBER VERB.NUMBER
  VERB_PHRASE.OBJECT unspecified return
  VERB_PHRASE end end.

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The dog likes a man.
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Knowledge base for the dogs world.
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Case frames for two verbs
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Semantic representation
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Concluding remarks

• The parse tree can be converted to a conceptual
  graph that represents the meaning of the
  sentence.
• Simpler approaches use templates and plug in
  words as they are recognized.
• Applications include
• Story understanding and question answering
• Front End to a database
• Information extraction and summarization on the
  web