CS544: Lecture 4: Reference and Other Problems

CS544: Lecture 4:Reference and Other Problems Jerry R. Hobbs USC/ISI Marina del Rey, CA March 3, 2011

Logical Form The x in Pat(x) and ask’(e1,x,y,e2) are the same. x The y and e2 in leave’(e2,y) and ask’(e1,x,y,e2) are the same. e2, y The y in Chris(y) and ask’(e1,x,y,e2) are the same. e2 y The e2 in leave’(e2,y) and early(e2) are the same. Pat asked Chris to leave early. Pat(x) & Past(e1) & ask’(e1,x,y,e2) & Chris(y) & leave’(e2,y) & early(e2) Now what?

An Ordinary Text Britons can’t say they weren’t warned. Much of David Cameron’s drastic reform program was outlined months ago in his party’s election manifesto, well before he was chosen as prime minister. No one paid much attention though: long experience has taught the country’s voters to regard campaign pledges as vague aspirations, not as commitments to immediate action. Besides, Cameron seemed like such a nice young man. He had remade the Tories’ image from a heartless pack of Thatcherite free-market ideologues to something gentler and more humane. He had visited the Arctic Circle to witness the effects of global warming. He had voted to recognize civil partnerships for gay and lesbian couples. Out went the flaming torch as the party’s emblem; in came the scribbly oak tree in eco-friendly green and blue.

An Ordinary Text Britons can’t say they weren’t warned. Of what? Much of David Cameron’s drastic reform program was outlined months ago in his party’s election manifesto, well before he was chosen as prime minister. No one paid much attention though: long experience has taught the country’s voters to regard campaign pledges as vague aspirations, not as commitments to immediate action. Besides, Cameron seemed like such a nice young man. He had remade the Tories’ image from a heartless pack of Thatcherite free-market ideologues to something gentler and more humane. He had visited the Arctic Circle to witness the effects of global warming. He had voted to recognize civil partnerships for gay and lesbian couples. Out went the flaming torch as the party’s emblem; in came the scribbly oak tree in eco-friendly green and blue.

An Ordinary Text Britons can’t say they weren’t warned. Much ofDavid Cameron’s drastic reform programwas outlined months ago in his party’s election manifesto, well before he was chosen as prime minister. No one paid much attention though: long experience has taught the country’s voters to regard campaign pledges as vague aspirations, not as commitments to immediate action. Besides, Cameron seemed like such a nice young man. He had remade the Tories’ image from a heartless pack of Thatcherite free-market ideologues to something gentler and more humane. He had visited the Arctic Circle to witness the effects of global warming. He had voted to recognize civil partnerships for gay and lesbian couples. Out went the flaming torch as the party’s emblem; in came the scribbly oak tree in eco-friendly green and blue. What’s the relation between reform and program and what is Cameron’s role in it? Is the reform or the program drastic? What does it mean for it to be drastic?

An Ordinary Text Britons can’t say they weren’t warned. Much of David Cameron’s drastic reform program was outlined months ago inhis party’s election manifesto, well before he was chosen as prime minister. No one paid much attention though: long experience has taught the country’s voters to regard campaign pledges as vague aspirations, not as commitments to immediate action. Besides, Cameron seemed like such a nice young man. He had remade the Tories’ image from a heartless pack of Thatcherite free-market ideologues to something gentler and more humane. He had visited the Arctic Circle to witness the effects of global warming. He had voted to recognize civil partnerships for gay and lesbian couples. Out went the flaming torch as the party’s emblem; in came the scribbly oak tree in eco-friendly green and blue. Same questions

An Ordinary Text tellbad thingbefore it happens Britons can’t say they weren’t warned. Much of David Cameron’s drastic reform program was outlinedmonths ago in his party’s election manifesto, well before he was chosen as prime minister. No one paid much attention though: long experience has taught the country’s voters to regard campaign pledges as vague aspirations, not as commitments to immediate action. Besides, Cameron seemed like such a nice young man. He had remade the Tories’ image from a heartless pack of Thatcherite free-market ideologues to something gentler and more humane. He had visited the Arctic Circle to witness the effects of global warming. He had voted to recognize civil partnerships for gay and lesbian couples. Out went the flaming torch as the party’s emblem; in came the scribbly oak tree in eco-friendly green and blue.

An Ordinary Text Britons can’t say they weren’t warned. Much of David Cameron’s drastic reform program was outlined months ago in his party’s election manifesto, well before he was chosen as prime minister. No one paid much attention though: long experience has taught the country’s voters to regard campaign pledges as vague aspirations, not as commitments to immediate action. Besides, Cameron seemed like such a nice young man. He had remade the Tories’ image from a heartless pack of Thatcherite free-market ideologues to something gentler and more humane. He had visited the Arctic Circle to witness the effects of global warming. He had voted to recognize civil partnerships for gay and lesbian couples. Out went the flaming torch as the party’s emblem; in came the scribbly oak tree in eco-friendly green and blue. to whom? by whom? to whom?

An Ordinary Text Britons can’t say they weren’t warned. Much of David Cameron’s drastic reform program was outlined months ago in his party’s election manifesto, well before he was chosen as prime minister. No one paid much attention though: long experience has taught the country’s voters to regard campaign pledges as vague aspirations, not as commitments to immediate action. Besides, Cameron seemed like such a nice young man. He had remade the Tories’ image from a heartless pack of Thatcherite free-market ideologues to something gentler and more humane. He had visited the Arctic Circle to witness the effects of global warming. He had voted to recognize civil partnerships for gay and lesbian couples. Out went the flaming torch as the party’s emblem; in came the scribbly oak tree in eco-friendly green and blue. How do these differ? How are they the same?

An Ordinary Text Britons can’t say they weren’t warned. Much of David Cameron’s drastic reform program was outlined months ago in his party’s election manifesto, well before he was chosen as prime minister. No one paid much attention though: long experience has taught the country’s voters to regard campaign pledges as vague aspirations, not as commitments to immediate action. Besides, Cameron seemed like such a nice young man. He had remade the Tories’ image from a heartless pack of Thatcherite free-market ideologues to something gentler and more humane. He had visited the Arctic Circle to witness the effects of global warming. He had voted to recognize civil partnerships for gay and lesbian couples. Out went the flaming torch as the party’s emblem; in came the scribbly oak tree in eco-friendly green and blue.

An Ordinary Text Britons can’t say they weren’t warned. Much of David Cameron’s drastic reform program was outlined months ago in his party’s election manifesto, well before he was chosen as prime minister. No one paid much attention though: long experience has taught the country’s voters to regard campaign pledges as vague aspirations, not as commitments to immediate action. Besides, Cameron seemed like such a nice young man. He had remade the Tories’ image from a heartless pack of Thatcherite free-market ideologues to something gentler and more humane. He had visited the Arctic Circle to witness the effects of global warming. He had voted to recognize civil partnerships for gay and lesbian couples. Out went the flaming torch as the party’s emblem; in came the scribbly oak tree in eco-friendly green and blue. They didn’t really lack hearts. Like wolves?

An Ordinary Text Britons can’t say they weren’t warned. Much of David Cameron’s drastic reform program was outlined months ago in his party’s election manifesto, well before he was chosen as prime minister. No one paid much attention though: long experience has taught the country’s voters to regard campaign pledges as vague aspirations, not as commitments to immediate action. Besides, Cameron seemed like such a nice young man. He had remade the Tories’ image from a heartless pack of Thatcherite free-market ideologues to something gentler and more humane. He had visited the Arctic Circle to witness the effects of global warming. He had voted to recognize civil partnerships for gay and lesbian couples. Out went the flaming torch as the party’s emblem; in came the scribbly oak tree in eco-friendly green and blue. Metonymy: “from the image of a heartless pack” Metonymy: members of pack are heartless, or Metaphor: pack is like an animal that can have a heart

An Ordinary Text Britons can’t say they weren’t warned. Much of David Cameron’s drastic reform program was outlined months ago in his party’s election manifesto, well before he was chosen as prime minister. No one paid much attention though: long experience has taught the country’s voters to regard campaign pledges as vague aspirations, not as commitments to immediate action. Besides, Cameron seemed like such a nice young man. He had remade the Tories’ image from a heartless pack of Thatcherite free-market ideologues to something gentler and more humane. He had visited the Arctic Circle to witness the effects of global warming. He had voted to recognize civil partnerships for gay and lesbian couples. Out went the flaming torch as the party’s emblem; in came the scribbly oak tree in eco-friendly green and blue. Before and after

An Ordinary Text Britons can’t say they weren’t warned. Much of David Cameron’s drastic reform program was outlined months ago in his party’s election manifesto, well before he was chosen as prime minister. No one paid much attention though: long experience has taught the country’s voters to regard campaign pledges as vague aspirations, not as commitments to immediate action. Besides, Cameron seemed like such a nice young man. He had remade the Tories’ image from a heartless pack of Thatcherite free-market ideologues to something gentler and more humane. He had visited the Arctic Circle to witness the effects of global warming. He had voted to recognize civil partnerships for gay and lesbian couples. Out went the flaming torch as the party’s emblem; in came the scribbly oak tree in eco-friendly green and blue. Why are these examples?

An Ordinary Text Britons can’t say they weren’t warned. Much of David Cameron’s drastic reform program was outlined months ago in his party’s election manifesto, well before he was chosen as prime minister. No one paid much attention though: long experience has taught the country’s voters to regard campaign pledges as vague aspirations, not as commitments to immediate action. Besides, Cameron seemed like such a nice young man. He had remade the Tories’ image from a heartless pack of Thatcherite free-market ideologues to something gentler and more humane. He had visited the Arctic Circle to witness the effects of global warming. He had voted to recognize civil partnerships for gay and lesbian couples. Out went the flaming torch as the party’s emblem; in came the scribbly oak tree in eco-friendly green and blue. Why is this a contrast? Color symbolism

Is There Systematicity? The basic unit of information is the predication: Cameron visited the Arctic Circle. Cameron(x) & Past(e) & visit’(e,x,y) & Arctic-Circle(y) Roughly one predicate per morpheme indicating the predicate-argument structure

Is There Systematicity? The basic unit of information is the predication: p(x,y) What is p? predicate strengthening What are x and y? coreference What’s the relation between p and x, p and y? In what way is it appropriate for p to describe x? y? metonymy, metaphor, ... p(x,y) & q(y,z) What’s the relation between these two predications? intraclausal coherence, discourse coherence (predicate strengthening on sentence adjacency)

What is the Argument?Coreference Pronouns: Britons can’t say they weren’t warned. Cameron’s program was outlined in his manifesto. Definite noun phrases: Anaphoric: the country, the country’s voters, the Tories Determinative: the Tories’ image Implicit arguments: they weren’t warned; outlined; Cameron was chosen prime minister Syntactic ambiguity: remade the image from ideologues to something humane: remade to something, image to something, or ideologues to something to(x,sthg): x = remade or x = image or x = ideologues?

Reference and Coreference Language: ......... x ................. y ............. World: A x refers to A; y refers to A; x and y corefer; y is coreferential with x The more general expressions (pronouns, definite NPs) are called anaphoric expressions, or anaphora Varieties of coreference: Pronouns Definite NPs Other anaphora, e.g. “other” anaphora Implicit arguments Many syntactic/attachment ambiguities

Coreference Coreference should not be thought of as a relation among words and phrases: A man in his own house is happy. A man in (a man in his own house)’s own house is happy. A man in (a man in (a man in his own house)’s own house)’s own house is happy. Rather it is an identity relation among variables: ... & man(x1) & in(x1,h1) & he(x2) & Poss(x2,h1) & house(h1) & ...  x1 = x2

An Algorithm for Pronoun Resolution S From pronoun: 1. Skip reflexive level 2. Go up to next NP or S 3. Breadth-first search for candidate NPs 4. Rule out if selectional, number or gender conflict 5. Pick the first candidate NP VP The network system NP PP divides data into NP small blocks SBAR VP called NP which S packets NP VP 80-90% accuracy it sends (Hobbs, 1976) The network system divides data into small blocks called packets, which it sends individually.

Problems with Algorithm Assumes parse tree is completely correct Best parsers are 90% bracket recall, 35-40% completely correct Best pronoun resolution today is 70-75% Doesn’t exploit current availability of large annotated corpora and statistical techniques Doesn’t even attempt to handle event pronouns. He visited the Arctic Circle. But it was only to win votes.

Resolving Event Pronouns (Chen Bin, Su Jian, and Tan Chew Lin, COLING 2010) “it”, “this” and “that” referring back to verb or nominalization, in OntoNotes annotated corpus; 15-20% of pronoun occurrences Baseline: most recent verb: F-score = 4% Best previous performance: F-score = 11% Principal features: Distance in sentences and words Syntactic role: subject/object in main/subordinate clause Immediate context: “it leads to ...” Path through parse tree between pronoun and candidate antecedent; plus top-level intervening nodes Results: F-score: 58%

If We Understood the Text ... Pronouns are used because the context and the rest of the text makes a more descriptive NP unnecessary. If we understood the context and the rest of the text, pronoun resolution would simply “fall out”. the Voyager 2 spacecraftspedthroughthe Saturnian system itcamewithin 90,000 kilometers ofthe moon Enceladus He hadn’tplanned to toss herhere. He had hoped to do itearlier in the voyage, between Nassau and San Juan. CONTRAST CONTRAST

First and Second Person Pronouns I, me, my: “.... I ....,” Person Verb[say] ... OR the speaker/writer: “I would momentarily forget where I was” we, us, our: “ .... we ....,” Verb[say] Person of Org OR the reader and/or writer: “We will not cover it here” OR the relevent everyone: “We had no idea what we had missed” you, your: “ ... you ...,” Person said. Person(s) being addressed in a quote / some nearby Person not coreferential with speaker OR the reader/listener OR anyone / impersonal

“the” and “a” Conventional notation: A car arrives. ==> (E x)[car(x) & arrive(x)] The car arrives. ==> arrive(  x [car(x)]) iota operator: the x such that car(x) But “the” and “a” convey information: “the”: the entity referred to by the NP is mutually identifiable in context via the property conveyed by the rest of the NP. The car is in the driveway. Known entity “a”: the entity referred to by the NP is not mutually identifiable in context via the property conveyed by the rest of the NP. A car is in the driveway. New entity Arnold Schwarzenegger is a short man. New property My approach: the man ==> the(x,e) & man’(e,x) a man ==> a(x,e) & man’(e,x) Highly idiosyncratic

Definite NPs Heuristic: Person resolves to last Person, etc. Several cases: Refers to something explicit in previous text: “I saw Bill Russell on a plane. The man is very tall.” “I bought a Prius. The car’s failures worry me.” Refers to something implied by something explicit in previous text: “The city was all quiet. The streets were covered in snow.” “ ... shaking my car acrossthe lane dividers” Anaphoric No good heuristics; there are efforts to learn common associations, e.g., part-of relations

Definite NPs Definite description is self-contained (determinative definite NP), because: It refers to something unique in the world: “the world” It refers to something uniquely associated with a syntactically related entity: “the wayWall Street operates”, “the topof a table” “the studentwho scored the best on the test” Superlatives: “the most momentous thing ...” Refers to something unique in the context: “the city turned monochrome” Generic: refers to the representative element of the set of all things of that description: “the dollar fell yesterday” = dollars Heuristic: If there is a superlative or right modifier Bad heuristic: if there is no antecedent in the previous text (determinatives far more frequent)

What is the Predicate? Interpreting compound nominals: reform program => reform(y) & nn(y,x) & program(x) election manifesto, campaign pledges, free-market ideologues Interpreting possessives: Cameron’s reform program, the Tories’ image, the party’s emblem Interpreting “of”: the effects of global warming, the city of London Interpreting other prepositions: outlined in the manifesto, remade the image from a heartless pack to something more humane Interpreting other underspecified predicates: out went the torch, in came the oak tree Lexical disambiguation: as bright as snow vs. as bright as Einstein Text gives us general predicates that we understand specifically.

Interpreting Nominal Compounds (Stephen Tratz and Ed Hovy, ACL2010) Corpus of 17,500 noun compounds from NY Times etc. Annotated with 43 relations: Purpose/Activity: Perform/EngageIn: cooking pot Create/Provide: nicotine patch Supervise: ethics board Location: hillside home Topic: Topic of Conversation: travel story Topic of Plan: loan terms Attribute: street name Coreferential: fighter plane Best features for machine learning: WordNet hypernyms; words in WordNet glosses Results: 79.3% accuracy

Why this Predicate with this Argument? p(x) interpreted as q(x) where p(x) --> q(x) Finding relevant aspect of predicate: drastic reform program: what part of a reform program can be drastic? vague aspirations Metaphor interpretation: a pack of ideologues: what aspect of packs is relevant here? Metonymy interpretation: “The pension fund, which has lost a quarter of its value, is planning ...” fund as amount of money vs. fund as organization p(x) interpreted as p(f(x))

Are the Predicate and Argument“Congruent”? p(x) The predicate really means something else, e.g., metaphor The argument really refers to something else: metonymy I like to read Shakespeare ==> I like to read the plays written by Shakespeare This restaurant takes American Express ==> This restaurant takes credit cards issued by American Express John is an elephant ==> John is big / clumsy / has a good memory / ... What about -- America believes in democracy.

Metonymy Metonymy: referring to something by referring to something related to it. We have to coerce the apparent referent into the actual referent via some coercion function. Common coercions: Entity into part of entity: ... researchers excavating a cave ... Organization into person: The White House said in its report that .... Container into contained: She had consumed three glasses.

Resolving Metonymy For a particular domain, you can have a graph of the principal types of entities, where the links between nodes are the possible relations between them. To resolve metonymy, find the shortest path from the node of the apparent referent to a node matching the required type. Country Organization See Katja Markert and Udo Hahn, Artificial Intelligence Journal, 2003 isa member-of rules Government Person e.g., France criticized American policy in Iraq. More generally, prove there is a relation between the apparent referent and something satisfying the requirements, in the most economical way. coercion relation read Shakespeare wrote plays text

Metaphor Metaphor: a predicate appropriate in one domain is used in another; abstract properties of that predicate are intended to be conveyed; sometimes large scale frameworks are enlisted (Lakoff & Johnson) Holding/Having is Perceiving: returned a handful of images Influence as Physical Force: CalPERS pushed companies to improve their governance. tougher regulation by federal agencies Knowledge as Visibility/Seeing: greater openness in the way companies are run delve into some controversial investments

Clause-Internal Coherence Relations that go beyond the predicate-argument relations conveyed by syntactic structure: Contrast: long experience has taught the country’s voters to regard campaign pledges as vague aspirations, not as commitments to immediate action. He had remade the Tories’ image from a heartless pack of Thatcherite free-market ideologues to something gentler and more humane. Causality: Much of David Cameron’s drastic reform program was outlined months ago in his party’s election manifesto, well before he was chosen as prime minister

Discourse Coherence Relations between successive segments of discourse are typically varieties of rephrasing/elaboration: Britons can’t say they weren’t warned. Much of David Cameron’s drastic reform program was outlined months ago in his party’s election manifesto, well before he was chosen as prime minister. similarity and contrast, generalization and examplification: He had visited the Arctic Circle to witness the effects of global warming. He had voted to recognize civil partnerships for gay and lesbian couples. successive changes of state, occasion: Out went the flaming torch as the party’s emblem; in came the scribbly oak tree in eco-friendly green and blue. causality, enablement, violated causality or implication: Britons can’t say they weren’t warned. No one paid much attention though:

Discourse Structure Britons can’t say they weren’t warned. Much of David Cameron’s drastic reform program was outlined months ago in his party’s election manifesto, well before he was chosen as prime minister. No one paid much attention though: long experience has taught the country’s voters to regard campaign pledges as vague aspirations, not as commitments to immediate action. Besides, Cameron seemed like such a nice young man. He had remade the Tories’ image from a heartless pack of Thatcherite free-market ideologues to something gentler and more humane. He had visited the Arctic Circle to witness the effects of global warming. He had voted to recognize civil partnerships for gay and lesbian couples. Out went the flaming torch as the party’s emblem; in came the scribbly oak tree in eco-friendly green and blue. Elab Viol Exp Expl Sim Elab Example Sim then, Contr

Penn Discourse TreeBank Kevin Knight: “Once you’ve defined the problem, there will be hundreds of solutions.” (Penn TreeBank --> statistical parsers) Penn Discourse TreeBank aims to annotate the 1M-word WSJ corpus with discourse relations between clauses and larger segments of discourse If explicit, tag them. If implicit, hypothesize and tag them. Label the arguments (discourse segments) Relations: Temporal (e.g., succession) Contingency (e.g., cause) Comparison (e.g., contrast) Expansion (e.g., generalization) The next 10 years should see significant advances in statistical discourse parsers.

Interpretation as Abduction 1. Represent the content as predications (the logical form). 2. Prove them, using the axioms in the knowledge base. 3. Allow assumptions in the proof, at a cost. 4. Pick the lowest cost proof. Speaker Hearer MB Utt Uniform framework for syntax, semantics, and pragmatics

Example The Boston office called. “Local Pragmatics” Problems illustrated: 1. Definite Reference: What does the Boston office refer to? 2. Interpreting compound nominals: What is the implicit relation between Boston and office? 3. Metonymy: Coerce from the Boston office to someone at the Boston office.

The Example Interpreted The Boston office called. LF: call'(e,x) & person(x) & rel(x,y) & office(y) & Boston(z) & nn(z,y) KB: person(J) work-for(J,O), office(O) work-for(x,y) --> rel(x,y) in(O,B), Boston(B) in(y,z) --> nn(z,y) New Information Definite Reference Metonymy Compound Nominal “Local Pragmatics” problems solved as a by-product Syntax : Parse Tree :: Interpretation : Proof Graph

Definite Reference John bought a new car. The engine is already broken. LF: . . . & car(c) & . . . . . . & engine(y,x) & . . . KB: car(x) --> engine(y,x) x=c

Definite Reference John bought a new car. The engine is already broken. LF: . . . & car(c) & . . . . . . & engine(y,x) & . . . KB: car(x) --> engine(y,x) Definite Reference with Implicature: John walked into the room. The chandelier shone brightly. LF: . . . & room(r) & . . . . . . & chandelier(y) & . . . KB: room(x) --> light(y) & in(y,x) light(y) & branching-fixtures(y) --> chandelier(y)

Lexical Ambiguity The plane taxied to the terminal. LF: plane(x) & taxi(x,y) & terminal(y) KB: airplane(x) --> plane(x) move-on-ground(x,y) & airplane(x) --> taxi(x,y) airport-terminal(y) --> terminal(y) airport(z) --> airplane(x) & airport-terminal(y) wood-smoother(x) --> plane(x) ride-in-cab(x,y) & person(x) --> taxi(x,y) computer-terminal(y) --> terminal(y)

Lexical Ambiguity John wanted a loan. He went to the bank. LF: . . . & loan(l) & . . . . . . & bank(y) & . . . KB: loan(x) --> financial-institution(y) & issue(y,x) financial-institution(y) & etc4(y) --> bank1(y) bank1(y) --> bank(y) river(z) --> bank2(y) & borders(y,z) bank2(y) --> bank(y)

CS544: Lecture 4: Reference and Other Problems