Csci 4152: Statistical Natural Language Procesing

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Linguistic Essentials
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Parts of Speech and Morphology

• Parts of Speech correspond to syntactic or
  grammatical categories such as noun, verb,
  adjectives and prepositions.
• Word categories are systematically related by
  morphological processes such as the formation of
  plural form from the singular form.

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Parts of Speech

• Nouns, verbs, adjectives
• Determiners
• Adverbs She ran very quickly She often travels
  to Vegas She started off impressively.
• Preposition She looked up the tree
• Particles She looked up the number
• Conjunctions, complementizer Funny but stupid She
  is afraid that .

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Syntax or Phrase Structure A simple context-free
grammar

• S --gt NP VP
• NP --gt DT NNS
• DT NN
• NP PP
• VP --gt VP PP
• VBD
• VBD NP
• P --gt IN NP

• DT --gt the
• NNS --gt children
• students
• mountains
• VBD --gt slept
• ate
• saw
• IN --gt in
• of
• NN --gt cake

The Grammar
The Lexicon
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Syntax or Phrase Structure A Parse Tree
S
NP VP AT
NNS VBD NP The
children ate AT NN

the cake
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Local and Non-Local Dependencies

• Dependencies may be local e.g., DT NNS
• A non-local dependency is an instance in which
  two words can be syntactically dependent even
  though they occur far apart in a sentence (e.g.,
  subject-verb agreement wh-extraction).
• Non-local phenomena are a challenge for certain
  statistical NLP approaches (e.g., n-grams) that
  model local dependencies.

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Semantic Roles

• Most commonly, noun phrases are arguments of
  verbs. These arguments have semantic roles the
  agent of an action, the patient and other roles
  such as the instrument or the goal.

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Subcategorization

• Different verbs can relate different numbers of
  entities transitive versus intransitive verbs.
• Verbs are classified according to the type of
  complements they permit. This called
  subcategorization.
• FrameNet combines semantic roles and
  subcategorization. Lets look up put.v

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Attachment Ambiguity and Garden-Path Sentences

• Attachment ambiguities occur with phrases that
  could have been generated by two different nodes
  in the parse tree. E.g. The
  children ate the cake with a spoon.
• Garden-Path sentences are sentences that lead you
  along a path that suddenly turns out not to
  work.
  E.g. The horse raced past the barn fell.

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Semantics

• Semantics is the study of the meaning of words,
  constructions, and utterances.
• Semantics can be divided into two parts lexical
  semantics and combination semantics.
• Lexical semantics hypernymy, hyponymy, antonymy,
  meronymy, holonymy, synonymy, homonymy, polysemy
  (no need to memorize!).
• Compositionality the meaning of the whole is
  built up from the meanings of its parts different
  from its parts.
  (More on the next slide)

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SemanticsIdea of Strict Compositionality

• The overall meaning of a phrase or sentence
  derives from the meanings of the constituent
  parts and the particular grammatical ways in
  which the parts are put together.
• Lets consider examples using the context free
  grammar we saw earlier

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Syntax or Phrase Structure A simple context-free
grammar

• S --gt NP VP
• NP --gt DT NNS
• DT NN
• NP PP
• VP --gt VP PP
• VBD
• VBD NP
• P --gt IN NP

• DT --gt the
• NNS --gt children
• students
• mountains
• VBD --gt slept
• ate
• saw
• IN --gt in
• of
• NN --gt cake

The Grammar
The Lexicon
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• While the constituent parts of a sentence and its
  grammatical structure are important for
  determining its meaning, strict compositionality
  often breaks down
• Idioms are one area of language where meanings
  are not compositional to be at a crossroads
  means facing a decision or choice

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Pragmatics

• Pragmatics is the area of studies that goes
  beyond the study of the meaning of a sentence and
  tries to explain what the speaker really is
  expressing.
• Understand the scope of quantifiers, speech acts,
  discourse analysis, anaphoric relations.