DOC PREVIEW
MIT 6 863J - Lecture 12: Featured attraction

This preview shows page 1-2-3-4-30-31-32-33-34-62-63-64-65 out of 65 pages.

Save
View full document
View full document
Premium Document
Do you want full access? Go Premium and unlock all 65 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 65 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 65 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 65 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 65 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 65 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 65 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 65 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 65 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 65 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 65 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 65 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 65 pages.
Access to all documents
Download any document
Ad free experience
Premium Document
Do you want full access? Go Premium and unlock all 65 pages.
Access to all documents
Download any document
Ad free experience

Unformatted text preview:

6.863J Natural Language ProcessingLecture 12: Featured attractionInstructor: Robert C. [email protected]•863J/9•611J SP04 Lecture 12The Menu Bar• Administrivia:• 3a due Friday; Lab 3b out Weds; due after vacationAgenda:Parsing strategies: Honey, I shrank the grammar!Features6•863J/9•611J SP04 Lecture 12Why: recover meaning from structureJohn ate ice-cream → ate(John, ice-cream)-This must be done from structure -Actually want something like λxλy ate(x,y)How?6•863J/9•611J SP04 Lecture 12Why: recover meaning from structureSNP VPVNPJohnateice-cream= λy.ate (y, ice-cream)VP(NP)= ate (john , icecream)ice-creamjohnλxλy.a t e (y , x )6•863J/9•611J SP04 Lecture 12Two parts:• Syntax: define hierarchical structure• Semantics: interpret over hierarchical structure• What are the constraints?6•863J/9•611J SP04 Lecture 12Conclusion we will head to• If we use too powerful a formalism, it lets us write ‘unnatural’ grammars• This puts burden on the person writing the grammar – which may be ok.• However, child doesn’t presumably do this (they don’t get ‘late days’)• We want to strive for automatic programming – ambitious goal6•863J/9•611J SP04 Lecture 12Key elements – part 1• Establish basic phrase types: S, VP, NP, PP, …• Where do these come from???6•863J/9•611J SP04 Lecture 12What kindsof phrases are there?• Noun phrases, verb phrases, adjectival phrases (“green with envy”), adverbial phrases (“quickly up the hill”), prepositional phrases (“off the wall”), etc.• In general: groundedon lexical items• Shows us the constraintson context-free rules for natural grammars• Example:6•863J/9•611J SP04 Lecture 12Phrase types are constrained by lexical projectionVerb Phrase → Verb Noun Phrase “is-a” (“kick the ball”)Prepositional Phrase →Preposition Noun Phrase(“on the table”)Adjective Phrase → Adjective Prep. Phrase(“green with envy”)Etc. … what is the pattern?6•863J/9•611J SP04 Lecture 12Function-argument relationXP →X arguments, where X= Noun, Verb, Preposition, Adjective (all lexical categories in the language)Like function-argument structure(so-called “Xbar theory”)Constrains what grammar rules cannotbe:Verb Phrase →Noun Noun Phraseor evenVerb Phrase →Noun Phrase Verb Noun Phrase6•863J/9•611J SP04 Lecture 12English is function-argument formfunctionatargsgreensoldthe stocka bargain pricewith envytheover-priced stock6•863J/9•611J SP04 Lecture 12Other languages are the mirror-inverse: arg-functionatgreensoldthe stocka bargain pricewith envytheover-priced stockThis is like Japanese6•863J/9•611J SP04 Lecture 12Key elements – part 2• Establish verb subcategories• What are these?• Different verbs take different # arguments• 0, 1, 2 arguments (‘complements’)• Poirot thought; Poirot thought the gun; Poirot thought the gun was the cause.• Some verbs take certain sentence complements:•I know who John saw/? I think who John sawpropositional types: • Embedded questions: I wonder whether…• Embedded proposition: I think that John saw Mary6•863J/9•611J SP04 Lecture 12Key elements• Subtlety to this• Believe, know, think, wonder,…• ? I believe why John likes ice-cream• I know why John likes ice-cream• I believe that John likes ice-cream• I believe (that) John likes ice-cream• # args, type: Verb subcategories• How many subcategories are there?• What is the structure?6•863J/9•611J SP04 Lecture 12Idea for phrases• They are based on ‘projections’ of words (lexical items) – imagine features ‘percolating’ upknow [V +proposition]XP [ ]V +proposition6•863J/9•611J SP04 Lecture 12Heads of phrasesknow [V +proposition]V +proposition6•863J/9•611J SP04 Lecture 12The parse structure for ‘embedded’ sentencesI believe (that) John likes ice-creamSNP VPIVbelievethat J. likes ice-cream6•863J/9•611J SP04 Lecture 12New phrase type: S-barNP VPIVbelieveSSbarthat J. likes ice-cream6•863J/9•611J SP04 Lecture 12SbarVPVbelieveSbarthatComp SJ. likes ice-cream6•863J/9•611J SP04 Lecture 12SbarVPVbelieveSbarComp SJ. likes ice-creamε6•863J/9•611J SP04 Lecture 12In fact, true for all sentences…Comp SεSJ. likes ice-creamSbarJohn likes ice-creamWhy?6•863J/9•611J SP04 Lecture 12What rules will we need?• (U do it..)6•863J/9•611J SP04 Lecture 12Verb types - continued• What about:Clinton admires honesty/Honesty admires ClintonHow do we encode these in a CFG?Should we encode them?• Colorless green ideas sleep furiously• Revolutionary new ideas appear infrequently6•863J/9•611J SP04 Lecture 12Problems with this – how much info?6•863J/9•611J SP04 Lecture 12Agreement gets complex…POSSUBPOSGENDERNUMBERCASEPOSSGPOSSNPERSONTENSEDCOMPNEGVOICEVAR–Czech: AGFS3----1A----6•863J/9•611J SP04 Lecture 12Other sentence types• Questions: • Will John eat ice-cream?• Did John eat ice-cream?• How do we encode this?6•863J/9•611J SP04 Lecture 12`Empty’ elements or categories• Where surface phrase is displaced from its canonical syntactic position• Examples:• The ice-cream was eaten vs.• John ate the ice-cream• What did John eat?• What did Bill say that that John thought the cat ate?• For What x, did Bill say… the cat ate x• Bush is too stubborn to talk to• Bush is too stubborn [x to talk to Bush]• Bush is too stubborn to talk to the Pope• Bush is too stubborn [Bush to talk to the Pope]6•863J/9•611J SP04 Lecture 12More interesting clause types• Apparently “long distance” effects: ‘displacement’ of phrases from their ‘base’ positions1. So-called ‘wh-movement’:What did John eat ?2. Topicalization (actually the same)On this day, it snowed two feet.3. Other cases: so-called ‘passive’:The eggplant was eaten by John• How to handle this?6•863J/9•611J SP04 Lecture 12We can think of this as ‘fillers’ and ‘gaps’• Filler= the displaced item• Gap = the place where it belongs, as argument• Fillers can be NPs, PPs, S’s• Gaps are invisible- so hard to parse! (we have to guess)• Can be complex:Which book did you file__ without__ reading__ ?Which violins are these sonatas difficult to play__ on ___6•863J/9•611J SP04 Lecture 12Problems with this – how much info?• Even verb subcategories not obviousJohn gave Mary the book → NP NPJohn gave the book to Mary → NP PPBut:John donated


View Full Document

MIT 6 863J - Lecture 12: Featured attraction

Documents in this Course
N-grams

N-grams

42 pages

Semantics

Semantics

75 pages

Semantics

Semantics

82 pages

Semantics

Semantics

64 pages

Load more
Download Lecture 12: Featured attraction
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view Lecture 12: Featured attraction and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Lecture 12: Featured attraction 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?