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

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

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

3 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.

4 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.

5 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. 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?

6 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. Same questions

7 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. tell bad thing before it happens

8 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?

9 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?

10 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.

11 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?

12 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

13 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

14 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?

15 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

16 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

17 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)

18 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)

19 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?

20 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

21 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

22 An Algorithm for Pronoun Resolution The network system divides data into small blocks called packets, which it sends individually. S NP 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 80-90% accuracy VP The network system divides sendsit which packets called small blocks into NPPP NP SBAR S NPVP data VP NP (Hobbs, 1976)

23 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.

24 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%

25 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”. He hadn’t planned to toss her here. He had hoped to do it earlier in the voyage, between Nassau and San Juan. CONTRAST the Voyager 2 spacecraft sped through the Saturnian system it came within 90,000 kilometers of the moon Enceladus

26 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

27 “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

28 Definite NPs 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 across the lane dividers” Heuristic: Person resolves to last Person, etc. No good heuristics; there are efforts to learn common associations, e.g., part-of relations Anaphoric

29 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 way Wall Street operates”, “the top of a table” “the student who 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)

30 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)

31 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.

32 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

33 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)

34 Why this Predicate with this Argument? 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 q(x) where p(x) --> q(x) p(x) interpreted as p(f(x))

35 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 John is an elephant ==> John is big / clumsy / has a good memory /... 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 What about -- America believes in democracy.

36 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.

37 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 Government Organization Person rules isa member-of More generally, prove there is a relation between the apparent referent and something satisfying the requirements, in the most economical way. read Shakespeare text wrote plays coercion relation See Katja Markert and Udo Hahn, Artificial Intelligence Journal, 2003 e.g., France criticized American policy in Iraq.

38 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

39 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)

40 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

41 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:

42 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. then, Contr Sim Example Elab Sim Elab Viol Exp Expl

43 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.

44 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. Hearer Speaker MB Utt Uniform framework for syntax, semantics, and pragmatics

45 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.

46 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) Syntax : Parse Tree :: Interpretation : Proof Graph New Information Definite Reference Metonymy Compound Nominal “Local Pragmatics” problems solved as a by-product

47 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

48 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)

49 Lexical Ambiguity The plane taxied to the terminal. 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) LF:

50 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) & etc 4 (y) --> bank 1 (y) bank 1 (y) --> bank(y) river(z) --> bank 2 (y) & borders(y,z) bank 2 (y) --> bank(y)

51 Axiomatizing Event Words Core theories explicating change and cause Define words like block, delay, deliver, destroy, enter, escape, give, hit, manage, provide, ready, schedule, seize,.... by means of axioms E.g., enter(x,y) changeTo(e) & in’(e,x,y) deliver(x,y,z) cause(x,e1) & changeTo’(e1,e2) & have’(e2,z,y) block(x,e) cause(x,n1) & not’(n1,p1) & possible’(p1,e)

52 Textual Entailment T: Russia is blocking oil from entering Ukraine. H: Oil cannot be delivered to Ukraine. not’(n2,c2) & can’(c2,x2,d2) & deliver’(d2,x2,o2,u2) block’(b1,x1,e1) & enter’(e1,o1,u1)

53 Textual Entailment T: Russia is blocking oil from entering Ukraine. H: Oil cannot be delivered to Ukraine. not’(n2,c2) & can’(c2,x2,d2) & deliver’(d2,x2,o2,u2) block’(b1,x1,e1) & enter’(e1,o1,u1) cause’(c1,x1,n1) & not’(n1,p1) & possible’(p1,e1) cause’(d2,x2,c3) & changeTo’(c3,h2) & have’(h2,u2,o2) in’(h2,o2,u2) possible’(p1,c4) & cause’(c4,x3,e1) Axioms in core theories

54 A Causal Relation The police prohibited the women from demonstrating. They feared violence. Logical Form: prohibit'(p 1,p,d) & demonstrate'(d,w) & CoRel(p 1,f,p 1 ) & fear'(f,y,v) & violent'(v,z) cause(f,p 1 ) Knowledge Base: fear'(f,p,v) --> diswant'(d 2,x,v) & cause(f,d2) demonstrate'(d,w) --> cause(d,v) & violent'(v,z) cause(d,v) & diswant'(d 2,p,v) --> diswant'(d 1,p,d) & cause(d 2,d 1 ) diswant'(d 1,p,d) & authority(p) --> prohibit'(p 1,p,d) & cause(d 1,p 1 ) cause(e 1,e 2 ) & cause(e 2,e 3 ) --> cause(e 1,e 3 ) We also have to explain the adjacency of the two sentences Explanation pattern

55 Problems Need a large knowledge base of commonsense knowledge organized in a language-friendly way Convert existing resources into axioms Build such a knowledge base from scratch (scope similar to building WordNet, FrameNet) Efficient theorem-proving e.g., Markov logic networks are efficient, but not if there are axioms with existentials in consequents (A x) car(x) --> (E y) engine(y,x) Probabilistic semantics for abduction


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