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NLP and Speech 2004 English Grammar

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

2 Word Classes and POS Tagging

3 Word Classes morphological properties distributional properties
Sort 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 properties What other words or phrases can occur nearby? e.g. possesive pronoun before noun semantic coherence Classify according to similar semantic type. e.g. nouns refer to object-like entities

4 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

5 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

6 Open Class Words: Nouns
Nouns – denote objects, concepts, … Proper Nouns Names for specific individual objects, entities e.g. the Eiffel Tower, Dr. Kemke Common Nouns Names for categories or classes or abstracts e.g. fruit, banana, table, freedom, sleep, ... Count Nouns enumerable entities, e.g. two bananas Mass Nouns not countable items, e.g. water, salt, freedom

7 Open Class Words: Verbs
Verbs – 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

8 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

9 Open Class Words: Adverbs
Adverbs – denote modifications of actions (verbs), qualities (adjectives), e.g. walk slowly, heavily drunk Directional or Locational Adverbs Specify direction or location e.g. go home, stay here Degree Adverbs Specify extent of process, action, property e.g. extremely slow, very modest

10 Open Class Words: Adverbs 2
Manner Adverbs Specify manner of action or process e.g. walk slowly, run fast Temporal Adverbs Specify time of event or action e.g. yesterday, Monday

11 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, ...

12 Closed Word Class: Prepositions
Occur before noun phrases semantics: describe relations often spatial or temporal relations

13 Closed Word Class: Pronouns
Shorthand for referring to entity or event Semantics: reference to entity Personal Pronouns refer to persons or entities, e.g. you, he, it, ... Possessive Pronouns possession or relation between person and object, e.g. his, her, my, its, ... Wh-Pronouns reference in question or back reference, e.g Who did this ... Frieda, who is 80 years old ...

14 Closed Word Class: Conjunctions
Join two phrases, clauses, or sentences Subordinating conjunction for embedded phrases Semantics: difficult Coordinating Conjunction and, or, but, ... e.g. He takes the cat and the dog. He takes the dog and she takes the dog. Subordinating Conjunction that, ... e.g. He thinks that the cat is nicer than the dog.

15 Closed Word Class: Auxiliary Verbs
Mark semantic features of main verb Semantics: difficult Tense addition expressing present, past or future, ... e.g. He will take the cat home. Aspect addition expressing completion of action e.g. He is taking the cat home. (incomplete) Mood addition expressing whether action is necessary .. e.g. He can take the cat home. (possible)

16 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)

17 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

18 POS Tagging - Taggers Problems in POS Tagging: Ambiguity Methods:
Rule-Based Tagging input is string of words, output is tagged string Stochastic Tagging determines tags based on the probability of the occurrence of the tag, given the observed word, in the context of the preceding tags.

19 Sentence Level Constructs

20 Sentence Level Constructs I
declarative “This flight leaves at 9 am.” S → NP VP imperative “Book this flight for me.” S → VP

21 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

22 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

23 Noun Phrase Modification - Prenominal
determiner the, a, this, some, ... predeterminer all the flights cardinal numbers, ordinal numbers one flight, the first flight, ... quantifiers much, little

24 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

25 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 → GerundVP GerundVP → GerundV NP | GerundV PP | ... relative clause a flight that serves breakfast Nominal → Nominal RelClause RelClause → (who | that) VP

26 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.

27 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.

28 Verb Subcategorization + Complements
more forms VP  Verb PP PP I fly from Boston to Chicago.

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