ISO/TC37/SC4/WG2 WD SemAF - Discourse Structure , Oxford HASIDA Koiti AIST, Japan

Outline Introduction Discourse Graph: Semantic Structure Discourse Tree: Syntactic (Presentational) Structure Discourse Relation 2

ISO Context Status: WD NWI ballot for /-10 Experts Koiti Hasida (Japan): project leader Harry Bunt (Netherland) Jerry Hobbs (USA) Nancy Ide (USA) Rashmi Prasad (USA) Kiyong Lee (Korea) Roland Hausser (Germany) Claudia Soria (Italy) Eric de la Clergerie (France) Antonio Pareja Lora (Spain) 3

Objective and Scope annotation, production, translation, etc. of various types of documents annotation to video for generating multilingual subtitles extension of Twitter to support semantically structured discussion by introducing semantic relations among tweets semantic structure of discourse, consisting of eventualities and semantic relations (in particular discourse relations) among them discourse semantics not only in linguistic content but also in (possibly silent) video, hypertext, game, etc. documents without predefined total temporal ordering of presentation, such as hypertexts and games syntactic (presentational) structure of discourse, comprising discourse segments (phrases, clauses, sentences, video scenes, and so on) guideline to develop and maintain minimal set of discourse relations 4

Outline Introduction Discourse Graph: Semantic Structure Discourse Tree: Syntactic (Presentational) Structure Discourse Relation 5

Terms and Definitions (Semantics) eventuality*: event (possibly dialogue act), state (including claim, constraint, semantic relation (in particular discourse relation)), process, proposition, or their abstraction (type) discourse relation: semantic relation among eventualities? 6

Discourse Graph Logical Form of Discourse graph representing discourse semantics Nodes and links represent eventualities. Links represent semantic relations (in particular discourse relations) among eventualities. Representation of nodes may follow any scheme to describe semantic structure of eventualities. ISO (SemAF-DA) recommended for describing eventualities consisting of dialogue acts, communicative functions, propositional content, etc. Representation of coreference and anaphora is attributed to other framework on semantic representation. 7

Sample Discourse Graph 8 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 In order to realize ubiquitous information access, huge amount of content is necessary, so that authoring of content must be easy. Also in order to realize ubiquitous information access, retrieval must be quick and easy. So semantic annotation is necessary.

you slipped vegetables under the table do you remember? maybe Sparky lived so long causes content object Links May Connect Other Links because semantic relations are eventualitis. 9 Do you remember you slipped vegetables under the table? Maybe that’s why Sparky lived so long. thematic role

you slipped vegetables under the table do you remember? Sparky lived so long content causes maybe Reification 10 2nd object 1st

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 Hypernode A discourse graph may be embedded (as a hypernode) in a larger discourse graph. 11 hypernode

Outline Introduction Discourse Graph: Semantic Structure Discourse Tree: Syntactic (Presentational) Structure Discourse Relation 12

Terms and Definitions (Syntax; 1) discourse segment: part of discourse representing eventuality. discourse modifier: part of discourse not representing eventuality, comprising a dependent discourse connective and a discourse segment as its object (representing $2 of the associated discourse relation). The discourse segment modified by a discourse modifier represents $1 of the associated discourse relation. For instance, ‘because I’m sleepy’ is a discourse modifier consisting of dependent discourse connective ‘because’ and its object ‘I’m sleepy’. 13

Terms and Definitions (Syntax; 2) discourse connective: part of discourse representing a discourse relation without its arguments. A discourse connective is not a discourse segment. It need not be continuous. dependent discourse connective: discourse connective representing (not reified) discourse relation. independent discourse connective: discourse connective representing eventuality (reified discourse relation). discourse connective qualifier: part of discourse qualifying a discourse connective. A discourse connective and a discourse connective qualifier qualifying it constitute a larger discourse connective. For instance, ‘maybe that’s why’ is a discourse connective consisting of more basic discourse connective ‘that’s why’ and its qualifier ‘maybe’. 14

Discourse Tree Parse Tree of Discourse annotated tree structure of linearly-ordered discourse representing presentational structures of the discourse addresses presentational aspects including importance (nucleus/satellite distinction). abstract syntax straightforward to encode in LAF consistent with intra-sentential syntax harmonization requirements? with SynAF and other annotation practices 15

A minus sign is the inverse operator. Sample Discourse Tree 16 [ [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 object of a discourse connective is $2 of the discourse relation. A discourse modifier depends on $1 of the discourse relation. A pair of curly brackets encloses a discourse modifier. A pair of brackets encloses a discourse segment which is not a discourse modifier.

Intersentential (Anaphoric) Discourse Connective 1 is more general than 2? 1.[addition [Tom was tired]. Also [he was feverish].] 2.[ 1 Tom was tired]. [{addition Also 1 } he was feverish.] Another example: [contrast On the one hand, [Tom is hungry]. On the other, [Mary is thirsty].] 17

Intersentential (Anaphoric) Discourse Connective (cont.) [{content [ 1 But a strong level of investor withdrawal is much more unlikely this time around]}, fund managers said.] [-inference A major reason 1 is that [investors already have sharply scaled back their purchases of stock funds since Black Monday].] 18

Mapping from Discourse Tree to Discourse Graph dependent discourse connective -> link discourse modifier = dependent discourse connective + discourse segment -> link + $2 discourse segment headed by discourse segment independent discourse connective -> discourse graph with semantic head 19

Mapping from Discourse Tree to Discourse Graph (cont.) [ [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]}]}.]] 20 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

Outline Introduction Discourse Graph: Semantic Structure Discourse Tree: Syntactic (Presentational) Structure Discourse Relation 21

Minimizing Discourse Relation Set Concentrate on semantics. abstract away presentational aspects importance or headedness (nucleus/satellite distinction) maximize versatility of semantic representation (discourse graph) Maximally accommodate polymorphism. 22

Discourse Relations Are Semantic Also elaborations such as detail are semantic relations because they are defined in terms of semantic entailment, etc. 23 This is an old story. We' re talking about years ago before anyone heard of asbestos having any questionable properties. detail

Importance Abstract importance (nucleus/satellite distinction) away from discourse relation. Importance (what is semantic head) is attributed to syntax (presentation) of discourse tree. [ 1 {conflict Although [its rooms are small]}, the hotel is large.] [{So 1 } Tom will stay there]. [ 2 {conflict 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 24

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? e.g., purpose is better than means because purpose is in the same direction as causal and temporal ordering. 25

Polymorphism, Metonymy, and Projection Object/Eventuality similar dissimilar general-specific set-member whole-part example restatement comparison attribution-content means-purpose comment-topic Instance/Type purpose conditional unconditional Semantics/Pragmatics enablement inference Temporal Projection circumstance before-after until simultaneous domain=range 26

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}] 27

Instance/Type Some relations may concern both instances and types of eventualities. [Use the sword {purpose to [cut it]}]. [I worked hard {purpose to [pass the exam]}]. [{conditional If [you’re going to school]}, it’s eight o’clock]. 28

Semantics/Pragmatics enablement [{-enables Since [here’s coffee]}, it’s possible that [you drink it].] [ 1 Here’s coffee.] [{-enables So 1 } drink it]. The presence of coffee provides the precondition for the imperative. enables here’s coffee drink it. dialog act enables here’s coffee you drink it prop. content 29

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. 30

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 31

additive positive Elaboration: specific, part, step, object, member, example, extraction, minimum, detail, equivalent, definition Attribution: content Background: background, circumstance Comparison: similar, proportion Complement: supplement Additive: conjunction, addition Manner: manner negative Contrast: contrast, dissimilar, 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 32

Relation Naming Convention Subject and object of transitive verb are $1 and $1. causes, motivates, triggers, enables Relational noun indicates $2. part, member, example, detail, content, constraint, evaluation, background, manner Collective adjective or noun is symmetric relation. equivalent, similar, conjunction, disjunction, contrast, conflict Object of preposition or conjunction is $2. after, letAlone This is not only about discourse relations but about any relations. 33