WG2 PWI SemAF - Discourse Structure , Berlin HASIDA Koiti AIST, Japan

Introduction (Concerns) annotation, production, translation, etc. of documents discourse structures not only in linguistic content but also in (possibly silent) video, etc. documents without predefined total temporal ordering of presentation, such as hypertexts and games organization of discourse structures consisting of eventualities (or what represent them, such as sentences, clauses, phrases, video scenes, and so on) and discourse relations among them to minimize the set of discourse relations by attributing presentational information to other parts of discourse structures If the discourse structures of speech and other linguistic data contained in motion pictures were fitted to this scheme, then multilingual subtitles to these pictures could be composed for a reduced cost by means of some standardized tool for multilingual translation. 2

Scope To describe how discourse constituents (eventualities) are combined through (possibly implicit) discourse connectives (discourse relations) to constitute a discourse (its semantic content). Elaboration, etc. Criteria for including certain relations 3 typically sentences factual and inferential

Policies Minimize the set of discourse relations while addressing semantic differences. Concentrate on semantic content representation, minimizing presentational aspects (such as importance: nucleus/satellite distinction) and maximizing the versatility of the representation. Maximally accommodate polymorphism. Use discourse trees to encode presentational aspects. 4

Terms Event???: event (possibly dialogue act) or state or process or their abstraction (type) discourse relation: semantic relation among eventualities discourse graph: graph representing discourse semantics in which nodes represent eventualities and links among them represent discourse relations discourse tree (discourse annotation?): annotated tree structure of linearly- ordered discourse representing presentational structures of the discourse besides its semantic content 5

Discourse Relation relations among eventualities and/or their types [I worked hard {to pass the exam}]. factual and/or inferential. [[Tom came] {because [Mary came]}]. = [[I guess Tom came] {because [Mary came]}]. purpose event type ($2) event type ($2) event ($1) event ($1) -inference reason conclusion -causes cause result 6

authoring of content must be easy semantic annotation is necessary inference huge amount of content is necessary retrieval must be quick and easy realize ubiquitous information service purpose inference Discourse Graph 7

In previous annotation practices, discourse relation may concern not the whole apparent argument but its core wrapped in an attitude report, a modal operator, etc. Wrapped Arguments/Metonymy Remember all those vegetables you slipped under the table ? Remember all those vegetables you slipped under the table ? Maybe that’s why Sparky lived so long. Maybe that’s why Sparky lived so long. you slipped under the table Sparky lived so long causes 8

you slipped those vegetable under the table Discourse Graph is Explicit 9 remember? maybe Sparky lived so long causes content object

A minus sign is the inverse operator. Discourse Tree 10 [ [Semantic annotation is necessary {-inference because {conjunction [ 2 retrieval must be quick and easy] and [ 3 authoring of content must be easy]}}]. [ 2 Retrieval must be quick and easy {purpose in order to [ 0 realize ubiquitous information access]}]. [ 3 Authoring of content must be easy {-inference because [ 1 huge amount of content is necessary {purpose in order to [ 0 realize ubiquitous information access]}]}]. ] discourse connective discourse relation The arg. of a discourse connective is the 2 nd arg. of the discourse relation. A discourse connective depends on the 1st arg. of the discourse relation. A pair of curly brackets is a discourse constituent headed by a discourse connective.

Discourse Tree (cont.) Encodes presentational aspects including importance (nucleus/satellite distinction) possibly partially. The current syntax is not a serious proposal. It should be easy to come up with a LAF- based representation of DTs. Do we have to standardize it? Harmonization requirements? with SynAF and other annotation practices 11

Importance Abstract importance (nucleus/satellite distinction) away from discourse relation, as it’s a matter of presentation. [ 1 {Although its rooms are small}, the hotel is large]. [{So 1 } Tom will stay there]. [ 2 {Although the hotel is large}, its rooms are small]. [{So 2 } Mary won’t stay there]. the hotel is large its rooms are small conflict Tom will stay there Mary won’t stay there inference symmetric 12

Importance (cont.) Unification between inverse relations: means vs. purpose cause vs. result reason vs. conclusion attribution vs. content general vs. specific whole vs. part Any criterion under which to choose names and directions of these relations? 13

Polymorphism, Metonymy, and Projection Object/Eventuality similar dissimilar general-specific set-member whole-part example restatement comparison attribution-content means-purpose comment-topic Temporal Projection circumstance before-after until simultaneous Instance/Type purpose conditional unconditional Semantics/Pragmatics enablement domain=range 14

Object/Eventuality Some relations concern not only eventualities but also objects. comparison [Tom is taller {than Mary is tall}]. attribution-content [I believe {that he’s right}]. [the belief {that he’s right}] means-purpose [cut it {with this sword}] [cut it {by using this sword}] 15

Instance/Type Some relations may concern both instances and types of eventualities. purpose [I used this sword {to cut it}]. conditional [{If you’re going to school}, it’s eight o’clock]. 16

Semantics/Pragmatics enablement [ 1 Here’s coffee.] [{So 1 } drink it]. The fact that here’s coffee enables the precondition for the imperative. [{Since here’s coffee}, it’s possible that you drink it]. enables here’s coffee Drink it. dialog act enables here’s coffee you drink it sem. content 17

Temporal Projection [Tom came {at 8 o’clock}]. [Tom came {when Mary came}]. time (semantic role) time (semantic role) circumstance (discourse rel.) circumstance (discourse rel.) equality or Projection? equality or Projection? equality or projection? equality or projection? `time’ and `circumstance’ may be unified. 18

Taxonomy Ted Sanders’ 3 (out of 4) dimensions additive vs. causal positive vs. negative factual vs. inferential Cf. the other dimension concerns linear order basic vs. non-basic 19

additive positive Elaboration: specific, part, step, object, member, example, extraction, minimum, detail, restatement, definition Attribution: content Background: background, circumstance Comparison: similarity, proportion Complement: supplement Additive: coordination, addition Manner: manner negative Contrast: contrast, dissimilarity, disjunction, substitution Complement: constraint Comparison: comparison, preference causal positive Causality: causes, motivates, triggers Enablement: purpose, enables Inference: inference, explanation Evaluation: evaluation, interpretation, comment Condition: conditional negative Concession: conflict Condition: otherwise, unconditional, compromise 20

Granularity At most about 40 relations Relations vs. Discourse Connectives Rhetorical Structure Theory (RST) 40 ～ 80 relations Penn Discourse TreeBank (PDTB) 250 explicit connectives Ichikawa (1957, 1963, 1978) about 30 relations Only finitely many basic relations/connectives fifteen minutes after = fifteen minutes + after 21

/cause/ Definition Participant in an event (that may be animate or inanimate) that initiates the event, but that does not act with any intentionality or consciousness; it exists independently of the event. Source Adapted from: SIL ( ‘ Causer ’ ) and Sowa (2000) ( ‘ Effector ’ ) Explanation Except for the lack of intentionality of the participant, this semantic role is very similar to that of the agent and in fact shares all its other properties. The role of cause can often be identified with verbs of initiation, or causation, such as: ‘ to cause ’, ‘ to produce ’, ‘ to start ’, ‘ to originate ’, ‘ to occasion ’, ‘ to generate ’. Example “ The bomb [cause] started several secondary fires ” 22