Computational Models of Discourse and Dialogue 2011: Conversation in Social Media
Persuasion in Social Media • Persuasion and argumentation in social media websites and forums
NLDS Social Media Dialogue Data • Data collected in the last year in collaboration with FoxTree’s Lab &Anand’sSemLab • Convinceme.net • 4forums.org • Carm.org
Using Mechanical Turk to get labels • http://pcon.soe.ucsc.edu/mturk_external/123/123.php?pageId=1597&assignmentId=ASSIGNMENT_ID_NOT_AVAILABLE&hitId=1HNBWKACQBSEV0YDIOYSBWM1C0YNIP • http://pcon.soe.ucsc.edu/mturk_external/qr/qr.php?pageId=1398&assignmentId=ASSIGNMENT_ID_NOT_AVAILABLE&hitId=1CEJFP6T9BRSEF7QNPYEV9U37T7Y6W
Classic Models of Discourse and Dialogue Structure(Task Oriented Dialog, Newspaper texts) Marilyn Walker. CS245. April 1st, 2010
Dialogue Processing (circa 1988) • Grosz & Sidner 1986 • Planning, Grice • Mann & Thompson 1988 • Rhetorical Relations, Text Structure • Polanyi 1984 • Linguistic Discourse Model • Hobbs 1979 • Coherence Relations
Dialogue Processing (circa 1988) • Me 1989 • Starting my Ph.D. with Aravind Joshi and Ellen Prince • Science IS NOT a belief system • => Empirical Methods in Discourse
Empirical/Statistical Approaches in NLP • Penn Treebank first available ~ 1990 • Plenty of data for parsing and POS • But what about language behavior above the sentence? • What about interactive language? • 1993: NSF Workshop on Centering in Naturally Occurring Discourse => Walker, Joshi & Prince 1997 • 1995: AAAI Workshop on Empirical Methods in Discourse => Walker & Moore CL special issue • 1996: NSF Workshop on Discourse & Dialogue Tagging => DAMSL markup • NOW: there is virtually no work in NLP on discourse and dialogue that is not corpus based/empirical.
What is a dialogue model? • A model is an abstraction of a thing, simplified or dimensionally reduced • A good model should be simpler but capture the essence of the real thing. • A good dialogue model should be testable. It should make predictions. Its claims should be such that one should be able to prove whether or not it is correct. • A good dialogue model should lead to results that are more generalizable.
Dialogue Structure • What makes a text coherent? • What are discourse structures? • Theories of discourse structures • Approaches to build discourse structures
Discourse Coherence • Example: • (1) John hid Bill’s car keys. • (2) He was drunk. • (1) John hid Bill’s car keys. • (2) He likes junk food. • (1) George Bush supports big business. • (2) He’s sure to veto House Bill 1711. • Hearers try to find connections between utterances in a discourse. • The possible connections between utterances can be specified as a set of coherence relations.
Coherence relations (Hobbs,1979) • Result: S0 causes S1 • John bought an Acura. His father went ballistic. • Explanation: S1 causes S0. • John hid Bill’s car keys. He was drunk. • Parallel: S0 and S1 are parallel. • John bought an Acura. Bill bought a BMW. • Elaboration: S1 is an elaboration of S0. • John bought an Acura this weekend. He purchased it for $40 thousand dollars. • …
Discourse structure S1: John took a train to Bill’s car dealership. S2: He needed to buy a car. S3: The company he works for now isn’t near any public transportation. S4:He also wanted to talk to Bill about their softball leagues. ] Explanation
Discourse structure S1: John took a train to Bill’s car dealership. S2: He needed to buy a car. S3: The company he works for now isn’t near any public transportation. S4:He also wanted to talk to Bill about their softball leagues. ] ] Explanation Parallel
Discourse structure S1: John took a train to Bill’s car dealership. S2: He needed to buy a car. S3: The company he works for now isn’t near any public transportation. S4:He also wanted to talk to Bill about their softball leagues. ] ] Explanation Explanation ] Parallel
Discourse parsing Explanation (e1) S1 (e1) Parallel (e2;e4) Explanation (e2) S4 (e4) S2(e2) S3(e3)
Why compute discourse structure? • Natural language understanding • Summarization • Information retrieval • Natural language Generation • Reference resolution
Theories of discourse structure • Mann and Thompson’s Rhetorical structure theory (1988) • Grosz and Sidner’s Attention, intention and structure of discourse (1986) • Discourse TAG. Penn Discourse Treebank (PDTB) • We will read a lot of papers using DTAG and PDTB so am just going to talk about these ‘classic theories’ today.
Rhetorical structure theory (RST) • Mann and Thompson (1988) • One theory of discourse structure, based on identifying relations between parts of the text: • Defined 20+ rhetorical relations • Presentational relations: intentional • Subject matter relations: informational • Nucleus: central segment of text • Satellite: more peripheral segment • Relation definitions and more.
Presentational (intentional) relations • Those whose intended effect is to increase some inclination in the hearer. • Relations: • Antithesis - Justify • Background - Motivation • Concession - Preparation • Enablement: - Restatement • Evidence - Summary
Subject matter (information) relations • Those whose intended effect is that the hearer recognize the relation in question. • Relations • Circumstance - Otherwise • Condition - Purpose • Elaboration - Solutionhood • Evaluation - Unconditional • Interpretation - Unless • Means - Volitional cause • Non-volitional cause - Volitional result • Non-volitional result
Multinuclear relations • Contrast • Joint • List • Multinuclear restatement • Sequence
Some examples • Explanation: John went to the coffee shop. He was sleepy. • Elaboration: John likes coffee. He drinks it every day. • Contrast: John likes coffee. Mary hates it.
Discourse structure John likes coffee They argue a lot contrast cause elaboration Mary hates coffee. He drinks it every day
A relation: Evidence • (a) George Bush supports big business. • (b) He’s sure to veto House Bill 1711. • Relation Name: Evidence • Constraints on Nucl: H might not believe Nucl to a degree satisfactory to S. • Constraints on Sat: H believes Sat or will find it credible • Constraints on Nucl+Sat: H’s comprehending Sat in Sat increases H’s belief of Nucl. • Effect: H’s belief of Nucl is increased.
A relation: Volitional-Cause • (a) George Bush supports big business. • (b) He’s sure to veto House Bill 1711. • Relation Name: Volitional-Cause • Constraints on Nucl: presents a volitional action • Constraints on Sat: none. • Constraints on Nucl+Sat: Sat presents a situation that could have caused the agent of the volitional action in Nucl to perform the action. • Effect: H recognizes the situation presented in Sat as a cause for the volitional action presented in Nucl.
Another example S: (a) Come home by 5:00. (b) Then we can go to the hardware store before it closes. (c) That way we can finish the bookshelves tonight. (a) (a) (b) (c) motivation motivation (b) (c) condition condition
A Problem with RST(Moore & Pollack, 1992) • How many rhetorical relations are there? • How can we use RST in dialogues? • How do we incorporate speaker intentions into RST? • RST does not allow for multiple relations between parts of a discourse: informational and intentional levels must coexist.
Grosz and Sidner (1986) • Three components: • Linguistic structure • Intentional structure • Attentionalstate
Linguistic structure • The structure of the sequence of utterances that comprises a discourse. • Utterances form Discourse Segment (DS); and a discourse is made up of embedded DSs. • What exactly is a DS? • Any evidence that humans naturally recognize segment boundaries? • Do humans agree on segment boundaries? • How to find the boundaries automatically?
Intentional structure • Speakers in a discourse may have many intentions: public or private. • Discourse purpose (DP): the intention that underlies engaging in a discourse. • Discourse segment purpose (DSP): the purpose a DS. How this segment contributes to achieving the overall DP? • Two relations between DSPs: • Dominance: if DSP1 contributes to DSP2, we say DSP2 dominates DSP1. • Satisfaction-precedence: DSP1 must be satisfied before DSP2.
Attentional State • The attentional state is an abstraction of the participants’ focus of attention as their discourse unfolds. • The state is a stack of focus spaces. • A focus space (FS) is associated with a DS, and it contains DSP and objects, properties, and relations salient in the DS. • When a DS ends, its FS is popped. • When a DS starts, its FS is pushed onto the stack.
An example C1: I need to travel in May. A1: And, what day in May do you want to travel? C2: I need to be there for a meeting on 15th. A2: And you are flying into what city? C3: Seattle. A3: And what time would you like to leave Pittsburgh? C4: Hmm. I don’t think there are many options for non-stop. A4: There are three non-stops today. C5: What are they? …. DS1 DS2 DS0 DS3 DS4 DS5
Discourse structure with intention info • I0: C wants A to find a flight for C • I1: C wants A to know that C is traveling in May. • I2: A wants to know the departure date etc. • I3: A wants to know the destination • I4: A wants to know the departure time • I5: C wants A to find a nonstop flight DS0 DS1 DS3 DS4 DS2 DS5 C1 A1-C2 A2-C3 A3 C4-C7
Problems with G&S 1986 • Assume that discourses are task-oriented • Assume there is a single, hierarchical structure shared by speaker and hearer • Do people really build such structures when they speak? Do they use them in interpreting what others say?
LIMITED ATTENTION CONSTRAINTWalker 1993, 1996 • ellipsis interpretation • pronominal anaphora interpretation • inference of discourse relations between utterances A and B • B MOTIVATES A • B is EVIDENCE for A
How is attention modeled ? • Linear Recency • Hierarchical Recency
Centering • Centering is formulated as a theory that relates focus of attention, choice of referring expression, and perceived coherence of utterances, within a discourse segment [Grosz et al., 1995]. • Brennan, Walker & Pollard 1987: Centering theory of Anaphora Resolution
Centers cross segments • Centers continued over discourse segment boundaries with pronominal referring expressions whose form is identical to those that occur within a discourse segment. • (29) and he's going to take a pear or two, and then.. go on his way • (30) um but the little boy comes, • (31) and uh he doesn't want just a pear, • (32) he wants a whole basket. • (33) So he puts the bicycle down, • (34) and he.. • [Pear Stories, Chafe, 1980; Passonneau, 1995]: • => discourse segment boundary between (32) and (33). [Passonneau, 1995, Passonneau & Litman 1997] • [Walker et al., 1998], (33) realizes a CONTINUE transition, indicating that utterance (33) is highly coherent in the context of utterance (32).
Why is centering only within Segment? • It is not plausible that a different process than centering would be required to explain the relationship between utterances (32) and (33), simply because these utterances span a discourse segment boundary. • Centering is a theory that relates focus of attention, choice of referring expression, and perceived coherence of utterances, within a discourse segment [Joshi & Weinstein 1983, Grosz, Joshi & Weinstein, 1995],
Tasks • Identify units, e.g. discourse segment boundaries • Determine relations between segments • Determine intentions of the segments • Determine the attentional state • Methods: • Inference-based approach: symbolic • Cue-based approach: statistical
Inference-based approach • Ex: John hid Bill’s car keys. He was drunk. • X is drunk people do not want X to drive • People don’t want X to drive people hide X’s car key. • Abduction: • AI-complete: Require and utilize world knowledge.
Cue-based approach • Attentional state: • Attentional changes: • (push) now, next, but, …. • (pop) anyway, in any case, now back to, ok, fine,... • True interruption: excuse me, I must interrupt • Flashback: oops, I forgot • Intention: • Satisfaction-precedes: first, second, furthermore, …. • Dominance: for example, first, second, ….
Cues (cont) • Linguistic structure • Elaboration: for example, … • Concession: although • Condition: if • Sequence: and, first, second. • Contrast: and, … • …