WG2 PWI24617-5SemAF - Discourse Structure

20101014, BerlinHASIDA Koiti

hasida.k@aist.go.jpAIST, 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.

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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

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typically sentencestypically sentences

factual and inferentialfactual and inferential

PoliciesMinimize 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.

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TermsEvent???: 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

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Discourse Relationrelations 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]}].

purposepurpose event type($2)

event type($2)

event($1)

event($1)

-inference-inference reasonreasonconclusionconclusion

-causes-causes causecauseresultresult

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authoring of content must be easyauthoring of content must be easy

semantic annotation is necessarysemantic annotation is necessary

inferenceinference

inferenceinference

huge amount of content is necessaryhuge amount of content is necessary

retrieval must be quick and easyretrieval must be quick and easy

realize ubiquitous information servicerealize ubiquitous information service

purposepurpose

purposepurpose

inferenceinference

Discourse Graph

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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 vegetablesyou slipped under the table ?Remember all those vegetablesyou slipped under the table ?

Maybe that’s whySparky lived so long.Maybe that’s whySparky lived so long.

you slipped under the tableyou slipped under the table

Sparky lived so longSparky lived so long

causescauses

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you slipped those vegetable under the tableyou slipped those vegetable under the table

Discourse Graph is Explicit

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remember?remember?

maybemaybe

Sparky lived so longSparky lived so long

causescauses

contentcontent

objectobject

A minus sign is the inverse operator.A minus sign is the inverse operator.

Discourse Tree

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[ [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 connectivediscourse connective

discourse relationdiscourse relation

The arg. of a discourse

connective is the 2nd arg. of the

discourse relation.

The arg. of a discourse

connective is the 2nd arg. of the

discourse relation.

A discourse connective depends on the 1st 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.

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

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ImportanceAbstract 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]. [{So1} Tom will stay there].

[2 {Although the hotel is large}, its rooms are small]. [{So2} Mary won’t stay there].

the hotel is largethe hotel is large

its rooms are smallits rooms are small

conflictconflict

Tom will stay thereTom will stay there

Mary won’t stay thereMary won’t stay there

inferenceinference

inferenceinference

symmetricsymmetric

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Importance (cont.)

Unification between inverse relations:means vs. purposecause vs. resultreason vs. conclusionattribution vs. contentgeneral vs. specificwhole vs. part

Any criterion under which to choose names and directions of these relations?

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Polymorphism, Metonymy, and Projection

Object/Eventualitysimilardissimilargeneral-specificset-memberwhole-partexamplerestatementcomparisonattribution-contentmeans-purposecomment-topic

Temporal Projectioncircumstancebefore-afteruntilsimultaneous

Instance/Typepurposeconditionalunconditional

Semantics/Pragmaticsenablement

dom

ain

=ra

ng

e

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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}]

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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].

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Semantics/Pragmaticsenablement

[1Here’s coffee.] [{So1} 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].

enablesenableshere’s coffeehere’s coffee Drink it.Drink it.

dialog actdialog act

enablesenableshere’s coffeehere’s coffee you drink ityou drink it

sem. contentsem. content

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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 orProjection?equality orProjection?equality orprojection?equality orprojection?

`time’ and `circumstance’ may be unified.

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Taxonomy

Ted Sanders’ 3 (out of 4) dimensionsadditive vs. causalpositive vs. negativefactual vs. inferential

Cf. the other dimension concerns linear orderbasic vs. non-basic

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additivepositive

Elaboration: specific, part, step, object, member, example, extraction, minimum, detail, restatement, definition

Attribution: contentBackground: background, circumstanceComparison: similarity, proportionComplement: supplementAdditive: coordination, additionManner: manner

negativeContrast: contrast, dissimilarity, disjunction, substitutionComplement: constraintComparison: comparison, preference

causalpositive

Causality: causes, motivates, triggersEnablement: purpose, enablesInference: inference, explanationEvaluation: evaluation, interpretation, commentCondition: conditional

negativeConcession: conflictCondition: otherwise, unconditional, compromise 20