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.