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74.793 NLP and Speech 2004 English Grammar Describing Natural Language Syntax: Word Classes and English Grammar (Ch.8 and 9) Word Classes / Part-of-Speech Tagging CFG with Grammatical Extensions Sentence Structures Noun Phrase - Modifications

74.793 NLP and Speech 2004 English Grammar Describing Natural Language Syntax: Word Classes and English Grammar (Ch.8 and 9) Word Classes / Part-of-Speech

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Page 1: 74.793 NLP and Speech 2004 English Grammar Describing Natural Language Syntax: Word Classes and English Grammar (Ch.8 and 9) Word Classes / Part-of-Speech

74.793 NLP and Speech 2004English Grammar

Describing Natural Language Syntax: Word Classes and English Grammar (Ch.8 and 9)

• Word Classes / Part-of-Speech Tagging

• CFG with Grammatical Extensions• Sentence Structures• Noun Phrase - Modifications• Verb Phrase - Subcategorization

Page 2: 74.793 NLP and Speech 2004 English Grammar Describing Natural Language Syntax: Word Classes and English Grammar (Ch.8 and 9) Word Classes / Part-of-Speech

Word Classes and POS Tagging

Page 3: 74.793 NLP and Speech 2004 English Grammar Describing Natural Language Syntax: Word Classes and English Grammar (Ch.8 and 9) Word Classes / Part-of-Speech

Word ClassesSort words into categories according to:

• morphological properties Which types of morphological forms do they take?e.g. form plural: noun+s; 3rd person: verb+s

• distributional propertiesWhat other words or phrases can occur nearby?e.g. possesive pronoun before noun

• semantic coherenceClassify according to similar semantic type. e.g. nouns refer to object-like entities

Page 4: 74.793 NLP and Speech 2004 English Grammar Describing Natural Language Syntax: Word Classes and English Grammar (Ch.8 and 9) Word Classes / Part-of-Speech

Open vs. Closed Word Classes

Open Class Types

The set of words in these classes can change over time, with the development of the language, e.g. spaghetti, to download

Open Class Types:

nouns, verbs, adjectives, adverbs

Page 5: 74.793 NLP and Speech 2004 English Grammar Describing Natural Language Syntax: Word Classes and English Grammar (Ch.8 and 9) Word Classes / Part-of-Speech

Open vs. Closed Word Classes

Closed Class Types

The set of words in these classes are very much determined and hardly ever chnage for one language.

Closed Class Types:

prepositions, determiners, pronouns, conjunctions, auxiliary verbs, particles, numerals

Page 6: 74.793 NLP and Speech 2004 English Grammar Describing Natural Language Syntax: Word Classes and English Grammar (Ch.8 and 9) Word Classes / Part-of-Speech

Open Class Words: NounsNouns – denote objects, concepts, …

Proper NounsNames for specific individual objects, entitiese.g. the Eiffel Tower, Dr. Kemke

Common NounsNames for categories or classes or abstractse.g. fruit, banana, table, freedom, sleep, ...

Count Nounsenumerable entities, e.g. two bananas

Mass Nounsnot countable items, e.g. water, salt, freedom

Page 7: 74.793 NLP and Speech 2004 English Grammar Describing Natural Language Syntax: Word Classes and English Grammar (Ch.8 and 9) Word Classes / Part-of-Speech

Open Class Words: VerbsVerbs – denote actions, processes, states e.g. smoke, dream, rest, run

several morphological forms e.g.

non-3rd person - eat

3rd person - eats

progressive/ - eating present participle/ gerundive

past participle - eaten

Auxiliaries, e.g. be, as sub-class of verbs

Page 8: 74.793 NLP and Speech 2004 English Grammar Describing Natural Language Syntax: Word Classes and English Grammar (Ch.8 and 9) Word Classes / Part-of-Speech

Open Class Words: Adjectives

Adjectives – denote qualities or properties of objects, e.g. heavy, blue, content

most languages have concepts for

colour - white, green, ...

age - young, old, ...

value- good, bad, ...

not all languages have adjectives as separate class

Page 9: 74.793 NLP and Speech 2004 English Grammar Describing Natural Language Syntax: Word Classes and English Grammar (Ch.8 and 9) Word Classes / Part-of-Speech

Open Class Words: Adverbs

Adverbs – denote modifications of actions (verbs), qualities (adjectives), e.g. walk slowly, heavily drunk

Directional or Locational AdverbsSpecify direction or location e.g. go home, stay here

Degree AdverbsSpecify extent of process, action, property e.g. extremely slow, very modest

Page 10: 74.793 NLP and Speech 2004 English Grammar Describing Natural Language Syntax: Word Classes and English Grammar (Ch.8 and 9) Word Classes / Part-of-Speech

Open Class Words: Adverbs 2

Manner AdverbsSpecify manner of action or process e.g. walk slowly, run fast

Temporal AdverbsSpecify time of event or action e.g. yesterday, Monday

Page 11: 74.793 NLP and Speech 2004 English Grammar Describing Natural Language Syntax: Word Classes and English Grammar (Ch.8 and 9) Word Classes / Part-of-Speech

Closed Word Classes

Closed Class Types:

prepositions: on, under, over, at, from, to, with, ...

determiners: a, an, the, ...

pronouns: he, she, it, his, her, who, I, ...

conjunctions: and, or, as, if, when, ...

auxiliary verbs: can, may, should, are

particles: up, down, on, off, in, out,

numerals: one, two, three, ..., first, second, ...

Page 12: 74.793 NLP and Speech 2004 English Grammar Describing Natural Language Syntax: Word Classes and English Grammar (Ch.8 and 9) Word Classes / Part-of-Speech

Closed Word Class: Prepositions

Prepositions

Occur before noun phrases

semantics: describe relations

often spatial or temporal relations

Page 13: 74.793 NLP and Speech 2004 English Grammar Describing Natural Language Syntax: Word Classes and English Grammar (Ch.8 and 9) Word Classes / Part-of-Speech

Closed Word Class: PronounsPronouns Shorthand for referring to entity or eventSemantics: reference to entity

Personal Pronounsrefer to persons or entities, e.g. you, he, it, ...

Possessive Pronounspossession or relation between person and object,

e.g. his, her, my, its, ...

Wh-Pronounsreference in question or back reference, e.g.

Who did this ... Frieda, who is 80 years old ...

Page 14: 74.793 NLP and Speech 2004 English Grammar Describing Natural Language Syntax: Word Classes and English Grammar (Ch.8 and 9) Word Classes / Part-of-Speech

Closed Word Class: ConjunctionsConjunctions Join two phrases, clauses, or sentencesSubordinating conjunction for embedded phrasesSemantics: difficult

Coordinating Conjunctionand, or, but, ...e.g. He takes the cat and the dog.

He takes the dog and she takes the dog.

Subordinating Conjunctionthat, ...e.g. He thinks that the cat is nicer than the dog.

Page 15: 74.793 NLP and Speech 2004 English Grammar Describing Natural Language Syntax: Word Classes and English Grammar (Ch.8 and 9) Word Classes / Part-of-Speech

Closed Word Class: Auxiliary VerbsAuxiliary Verbs Mark semantic features of main verb Semantics: difficult

Tenseaddition expressing present, past or future, ...e.g. He will take the cat home.

Aspectaddition expressing completion of actione.g. He is taking the cat home. (incomplete)

Moodaddition expressing whether action is necessary ..e.g. He can take the cat home. (possible)

Page 16: 74.793 NLP and Speech 2004 English Grammar Describing Natural Language Syntax: Word Classes and English Grammar (Ch.8 and 9) Word Classes / Part-of-Speech

Closed Word Class: Copula

Copula and Modal Verbs• subclass of Auxiliary Verbs State or tense description or modality of action Semantics: difficult (e.g. modal logic)

State / Process: be and do

e.g. He is at home. He does nothing.

Tense: have

e.g. He has taken the cat home.

Modality: can, ought to, should, must

e.g. He can take the cat home. (possibility)

Page 17: 74.793 NLP and Speech 2004 English Grammar Describing Natural Language Syntax: Word Classes and English Grammar (Ch.8 and 9) Word Classes / Part-of-Speech

POS Tagging - Tagsets

Tagsets for English Penn Treebank, 45 tags

Brown corpus, 87 tags

C5 tagset, 61 tags

C7 tagset, 146 tags

For references see textbook, p.296

C5 and C7 tagsets are listed in textbook, Appendix C

Page 18: 74.793 NLP and Speech 2004 English Grammar Describing Natural Language Syntax: Word Classes and English Grammar (Ch.8 and 9) Word Classes / Part-of-Speech

POS Tagging - Taggers

Problems in POS Tagging:Ambiguity

Methods:Rule-Based Tagging

input is string of words, output is tagged stringStochastic Tagging

determines tags based on the probability of the occurrence of the tag, given the observed word, in the context of the preceding tags.

Page 19: 74.793 NLP and Speech 2004 English Grammar Describing Natural Language Syntax: Word Classes and English Grammar (Ch.8 and 9) Word Classes / Part-of-Speech

Sentence Level Constructs

Page 20: 74.793 NLP and Speech 2004 English Grammar Describing Natural Language Syntax: Word Classes and English Grammar (Ch.8 and 9) Word Classes / Part-of-Speech

Sentence Level Constructs I

Sentence Level Constructs I

declarative

“This flight leaves at 9 am.”

S → NP VP

imperative

“Book this flight for me.”

S → VP

Page 21: 74.793 NLP and Speech 2004 English Grammar Describing Natural Language Syntax: Word Classes and English Grammar (Ch.8 and 9) Word Classes / Part-of-Speech

Sentence Level Constructs II

Sentence Level Constructs II

yes-no-question

“Does this flight leave at 9 am?”

S → Aux NP VP

wh-question

“When does this flight leave Winnipeg?”

S → Wh-NP Aux NP VP

Page 22: 74.793 NLP and Speech 2004 English Grammar Describing Natural Language Syntax: Word Classes and English Grammar (Ch.8 and 9) Word Classes / Part-of-Speech

Noun Phrase Modification 1

Noun Phrase Modifiers

head = the central noun of the NP

modifiers = additions to head noun included in NP

• modifiers before the head noun (prenominal) • modifiers after the head noun (post-nominal)

examples: determiners, adjectives, PPs

e.g. the young man

the girl with the red hat

Page 23: 74.793 NLP and Speech 2004 English Grammar Describing Natural Language Syntax: Word Classes and English Grammar (Ch.8 and 9) Word Classes / Part-of-Speech

Noun Phrase Modification - Prenominal

determinerthe, a, this, some, ...

predeterminerall the flights

cardinal numbers, ordinal numbersone flight, the first flight, ...

quantifiersmuch, little

Page 24: 74.793 NLP and Speech 2004 English Grammar Describing Natural Language Syntax: Word Classes and English Grammar (Ch.8 and 9) Word Classes / Part-of-Speech

Noun Phrase Modification - Prenominal

adjectives

a first-class flight, a long flight

adjective phrase

the least expensive flight

Grammar Rule

NP → (Det) (Card) (Ord) (Quant) (AP) Nominal

Page 25: 74.793 NLP and Speech 2004 English Grammar Describing Natural Language Syntax: Word Classes and English Grammar (Ch.8 and 9) Word Classes / Part-of-Speech

Noun Phrase Modification - Postnominal prepositional phrase PP

all flights from Chicago

Nominal → Nominal PP (PP) (PP)

non-finite clause, gerundive postmodifers

all flights arriving after 7 pm

Nominal → GerundVPGerundVP → GerundV NP | GerundV PP

| ...

relative clause

a flight that serves breakfast

Nominal → Nominal RelClauseRelClause → (who | that) VP

Page 26: 74.793 NLP and Speech 2004 English Grammar Describing Natural Language Syntax: Word Classes and English Grammar (Ch.8 and 9) Word Classes / Part-of-Speech

Verb Subcategorization

Verb Phrase and Subategorization

VP = Verb + other constituents (complements)

Verb Subcategorization

Different verbs accept or need different constituents or complements.

Verbs can be classified according to the complements they accept or need.

Page 27: 74.793 NLP and Speech 2004 English Grammar Describing Natural Language Syntax: Word Classes and English Grammar (Ch.8 and 9) Word Classes / Part-of-Speech

Verb Subcategorization + Complements

sentential complement

VP Verb inf-sentence

I want to fly from Boston to Chicago.

NP complement

VP Verb NP

I want this flight.

no complement

VP Verb I sleep.

Page 28: 74.793 NLP and Speech 2004 English Grammar Describing Natural Language Syntax: Word Classes and English Grammar (Ch.8 and 9) Word Classes / Part-of-Speech

Verb Subcategorization + Complements

more forms

VP Verb PP PP

I fly from Boston to Chicago.