Presentation on theme: "NLP and Speech 2004 English Grammar"— Presentation transcript:
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 TaggingCFG with Grammatical ExtensionsSentence StructuresNoun Phrase - ModificationsVerb Phrase - Subcategorization
3 Word Classes morphological properties distributional properties Sort words into categories according to:morphological propertiesWhich types of morphological forms do they take?e.g. form plural: noun+s; 3rd person: verb+sdistributional propertiesWhat other words or phrases can occur nearby?e.g. possesive pronoun before nounsemantic coherenceClassify according to similar semantic type.e.g. nouns refer to object-like entities
4 Open vs. Closed Word Classes Open Class TypesThe set of words in these classes can change over time, with the development of the language, e.g. spaghetti, to downloadOpen Class Types:nouns, verbs, adjectives, adverbs
5 Open vs. Closed Word Classes Closed Class TypesThe 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 NounsNames for specific individual objects, entitiese.g. the Eiffel Tower, Dr. KemkeCommon NounsNames for categories or classes or abstractse.g. fruit, banana, table, freedom, sleep, ...Count Nounsenumerable entities, e.g. two bananasMass Nounsnot countable items, e.g. water, salt, freedom
7 Open Class Words: Verbs Verbs – denote actions, processes, statese.g. smoke, dream, rest, runseveral morphological forms e.g.non-3rd person - eat3rd person - eatsprogressive/ - eatingpresent participle/gerundivepast participle - eatenAuxiliaries, e.g. be, as sub-class of verbs
8 Open Class Words: Adjectives Adjectives – denote qualities or properties of objects, e.g. heavy, blue, contentmost languages have concepts forcolour - 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 drunkDirectional or Locational AdverbsSpecify direction or locatione.g. go home, stay hereDegree AdverbsSpecify extent of process, action, propertye.g. extremely slow, very modest
10 Open Class Words: Adverbs 2 Manner AdverbsSpecify manner of action or processe.g. walk slowly, run fastTemporal AdverbsSpecify time of event or actione.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, areparticles: up, down, on, off, in, out,numerals: one, two, three, ..., first, second, ...
12 Closed Word Class: Prepositions Occur before noun phrasessemantics: describe relationsoften spatial or temporal relations
13 Closed Word Class: Pronouns Shorthand for referring to entity or eventSemantics: reference to entityPersonal 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 ...
14 Closed Word Class: Conjunctions Join two phrases, clauses, or sentencesSubordinating conjunction for embedded phrasesSemantics: difficultCoordinating 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.
15 Closed Word Class: Auxiliary Verbs Mark semantic features of main verbSemantics: difficultTenseaddition 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)
16 Closed Word Class: Copula Copula and Modal Verbssubclass of Auxiliary VerbsState or tense description or modality of actionSemantics: difficult (e.g. modal logic)State / Process: be and doe.g. He is at home. He does nothing.Tense: havee.g. He has taken the cat home.Modality: can, ought to, should, muste.g. He can take the cat home. (possibility)
17 POS Tagging - Tagsets Tagsets for English Penn Treebank, 45 tags Brown corpus, 87 tagsC5 tagset, 61 tagsC7 tagset, 146 tagsFor references see textbook, p.296C5 and C7 tagsets are listed in textbook, Appendix C
18 POS Tagging - Taggers Problems in POS Tagging: Ambiguity Methods: Rule-Based Tagginginput is string of words, output is tagged stringStochastic Taggingdetermines tags based on the probability of the occurrence of the tag, given the observed word, in the context of the preceding tags.
20 Sentence Level Constructs I declarative“This flight leaves at 9 am.”S → NP VPimperative“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 VPwh-question“When does this flight leave Winnipeg?”S → Wh-NP Aux NP VP
22 Noun Phrase Modification 1 Noun Phrase Modifiershead = the central noun of the NPmodifiers = additions to head noun included in NPmodifiers before the head noun (prenominal)modifiers after the head noun (post-nominal)examples: determiners, adjectives, PPse.g. the young manthe girl with the red hat
23 Noun Phrase Modification - Prenominal determinerthe, a, this, some, ...predeterminerall the flightscardinal numbers, ordinal numbersone flight, the first flight, ...quantifiersmuch, little
24 Noun Phrase Modification - Prenominal adjectivesa first-class flight, a long flightadjective phrasethe least expensive flightGrammar RuleNP → (Det) (Card) (Ord) (Quant) (AP) Nominal
26 Verb Subcategorization Verb Phrase and SubategorizationVP = Verb + other constituents (complements)Verb SubcategorizationDifferent 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 complementVP Verb inf-sentenceI want to fly from Boston to Chicago.NP complementVP Verb NPI want this flight.no complementVP VerbI sleep.
28 Verb Subcategorization + Complements more formsVP Verb PP PPI fly from Boston to Chicago.