Introduction to Computational Linguistics

Introduction to Computational Linguistics

Introduction to Linguistics II Ling 2-121C, group b Lecture 5 Eleni Miltsakaki AUTH Spring 2006 1 Syntax review II What are heads and complements? Can you identify them in the phrases below? The man with the telescope

The destruction of Rome A person worthy of praise A boy who pitched a perfect game What do we mean by selectional restrictions of verbs? Are selectional restrictions applicable to verbs only? Can you give examples of selectional restrictions forced by other word classes? 2 Syntax review II What are phrase structure rules? Write 5 basic phrase structure rules for English

What are the two basic uses of phrase structure rules? What is recursion? When does it occur? Can you give some examples of recursive structures in English? 3 Exercise The girl with the feather on the ribbon on the brim Expand the above sentence with a recursive structure and show that in a tree

4 Syntax review II What are embedded structures? Give examples. What do we call center embedding? Give examples. Whats special about center embedding? 5 Sentence relatedness

Transformational rules A way to capture the relationship between a declarative and a question is to allow phrase structure to generate the structure using special rules: transformation rules Move Aux: take the first aux and move it to the left of the subject The boy is sleeping Is the boy ___ sleeping? 6 Deep and surface structure Deep structure: the basic structure

Surface structure: the resulting structure after applying a transformational rule The boys is sleeping: Deep Move Aux Is the boy sleeping? Surface 7 Other transformational rules Active passive (aka passivization) The cat chased the mouse The mouse was chased by the cat

There-sentences There was a man on the roof A man was on the roof PP-preposing The astronomer saw the star with the telescope With the telescope, the man saw the star 8 Syntactic dependencies Wh-questions

Who did Helen say the senator wanted to hire ___? Who did Helen say the senator wanted the congressional representative to try to hire ___? Who did Helen say the senator wanted the congressional representative to try to convince the Speaker of the House to get the Vice President to hire ___? Long-distance dependencies created by wh-movement are a fundamental part of human language. They provide evidence that sentences are not just strings of words but they are supported by rich phrase structure trees. These trees express the underlying structure of the sentence as well as their relation to

other sentences in the language 9 Universal grammar UG provides the basic design for human language Individual languages are variations on the basic design 10 Parameters

All languages have phrase structure rules All languages have heads and complements In some languages heads come before complements (English) In others, complements come before heads (Japanese). 11 Wh-islands Emily paid a visit to the senator who wants to hire who? *Who did Emily pay a visit to the senator that wants to hire ___?

Miss Marple asked Sherlock whether Poirot had solved the crime Who did Miss Marple ask ___ whether Poirot had solved the crime? *Who did Miss Marple ask Sherlock whether ___ had solved the crime? *What did Miss Marple ask Sherlock whether Poirot had solved ___? 12 Universal wh-islands Constraints against wh-movement depend

on structure, not length John ate bread and cheese (Coordinate). John ate bread with cheese (DO). *What did John eat bread and? What did John eat bologna with? 13 SEMANTICS 14 Intro to semantics

What is semantics? The study of the linguistic meaning of morphemes, words, phrases, and sentences. What is lexical semantics? The study of the meaning of words and the meaning relations among them.

What is phrasal or sentential semantics? The meaning of syntactic units larger than the word What is pragmatic meaning? The effect of context on sentence meaning. E.g., Its open here meaning Open the window 15

Lexical semantics Learning a language includes learning the agreedupon meanings of certain strings of sounds and how to combine these units into larger meaningful units. The meaning of words is part of linguistic knowledge/grammar. The mental storehouse of the info about words and morphemes is called the lexicon. 16 Semantic properties Example: assassin Person

Who murdered an important person Sharing properties Female: woman, aunt, mother, tigress, hen Human: doctor, bachelor, professor, baby Young: child, baby 17 Semantic properties Verbs Motion: bring, fall, walk, run Contact: hit, kick, kiss

Creation: build, imagine, make Sense: hear, see, feel 18 Semantic properties Evidence for semantic properties: errors Bridge of nose When my gums bled Bridge of neck When my tongues bled

He came too late Mary was young Thats a horse of another color He came too early Mary was early Thats a horse of another race 19

Semantic properties Attention! Do not confuse semantic properties of words with nonlinguistic properties. E.g., Water is composed of hydrogen and oxygen. But thats not part of the linguistic meaning of the word water. 20 Semantic properties

One way of representing semantic properties is by semantic features. Woman +female +human -young Father +male +human +parent

Girl +female +human +young Mare +female -human -young +equine 21

Homonyms Homonyms are different words that are pronounced the same: Tale tail To two too They may or may not have different spelling. Homonyms create ambiguity: Ill meet you by the bank, in front of the automated teller machine. Ill meet you by the bank. We can go fishing. 22

Polysemy When a word has multiple meanings it is polysemous. Bear=to tolerate, to carry, to support Bear is also a homonym: bear=wild animal 23 Heteronym Two words are heteronyms if they are spelled the same, but are pronounced

differently. Dove the bird Dove past tense of dive Lead the verb Lead the metal 24 Homographs Homographs are words that are spelled the same but have different meanings: Dove the bird Dove the past tense of dive

Bear the verb Bear the animal 25 Homonyms Heteronyms Homographs Pronounced

identically Yes No Yes/no Spelled identically Yes/no

Yes Yes 26 Synonyms Words that sound different but have the same (or almost the same) meaning are synonyms. Apathetic, phlegmatic, passive, sluggish,

indifferent Sofa, couch Degree of similarity depends on number of semantic properties that two words share 27 Antonyms Words that are opposite in meaning are antonyms Beautiful ugly (=not beautiful) Big small, hot cold

Gradable properties Tiny, small, medium, large, huge, gigantic not tiny doesnt mean gigantic. 28 Gradable antonyms Marked unmarked How high is the mountain? (not How low is the mountain?) high is the unmarked member of the pair high-low

29 Relational opposites Relational opposites display symmetry in their meaning: e.g., if X gives Y to Z then Z receives Y from X Give receive Buy sell Teacher pupil Comparative forms of gradable pairs of adjectives

often form relational pairs Mary is taller than Sally A Mercedes is more expensive than a Smart. 30 Relationships between certain semantic features can reveal knowledge about antonyms: A word that is [+married] is [-single] A word that is [+single] is [-married] 31

Autoantonyms The same word having two antonymic senses: To cleave: to split apart, to cling together To dust: to remove sth, to spread sth 32 Formation of antonyms

UnNonInDisMis- 33

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