ISO/TC37/SC4/WG2 WD24617-5 SemAF - Discourse Structure 2011-01-12, Oxford HASIDA Koiti [email protected] AIST, Japan

ISO/TC37/SC4/WG2 WD24617-5SemAF - Discourse Structure

2011-01-12, OxfordHASIDA Koiti

[email protected], Japan

Outline

IntroductionDiscourse Graph: Semantic

StructureDiscourse Tree: Syntactic

(Presentational) StructureDiscourse Relation

2

ISO ContextStatus: WD

NWI ballot for 2010-07/-10Experts

Koiti Hasida (Japan): project leaderHarry 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 Scopeannotation, production, translation, etc. of

various types of documentsannotation to video for generating multilingual

subtitlesextension 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 themdiscourse 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




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?

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Discourse GraphLogical Form of Discoursegraph representing discourse semanticsNodes 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 24617-2 (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

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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

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 tableyou slipped vegetables under the table

do you remember?do you remember?

maybemaybe

Sparky lived so longSparky lived so long

causescauses

contentcontent

objectobject

Links May Connect Other Links

because semantic relations are eventualitis.

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Do you remember you slipped vegetables under the table? Maybe that’s why Sparky lived so long.

thematic rolethematic role

you slipped vegetables under the tableyou slipped vegetables under the table

do you remember?do you remember?

Sparky lived so longSparky lived so long

contentcontent

causescauses maybemaybe

Reification

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2nd2nd

objectobject

1st1st

authoring of content must be easyauthoring of content must be easy


inferenceinference

inferenceinference

huge amount of content is necessaryhuge amount of content is necessary

retrieval must be quick and easyretrieval must be quick and easy


purposepurpose

purposepurpose

HypernodeA discourse graph may be

embedded (as a hypernode) in a larger discourse graph.

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hypernode

Outline




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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 Discourseannotated tree structure of linearly-

ordered discourse representing presentational structures of the discourse

addresses presentational aspects including importance (nucleus/satellite distinction).

abstract syntaxstraightforward to encode in LAF

consistent with intra-sentential syntaxharmonization requirements?

with SynAF and other annotation practices15

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

Sample 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 object of a discourse

connective is $2 of the 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 discourse modifier depends on $1 of the discourse

relation.

A pair of curly brackets encloses a discourse modifier.

A pair of curly brackets encloses a discourse modifier.

A pair of brackets encloses a discourse

segment which is not 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 Also1}

he was feverish.]Another example:[contrast On the one hand, [Tom is

hungry]. On the other, [Mary is thirsty].]

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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 reason1 is that [investors already have sharply scaled back their purchases of stock funds since Black Monday].]

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Mapping from Discourse Tree to Discourse Graph

dependent discourse connective-> link

discourse modifier= dependent discourse connective

+ discourse segment-> link + $2

discourse segment headed bydiscourse segmentindependent discourse connective-> discourse graph with semantic head

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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]}]}.]]

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authoring of content must be easy

authoring of content must be easy


inferenceinference

huge amount of content is necessary

huge amount of content is necessary

retrieval must be quick and easy

retrieval must be quick and easy


purposepurpose

purposepurpose

inferenceinference

Outline




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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.

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Discourse Relations Are Semantic

Also elaborations such as detail are semantic relations because they are defined in terms of semantic entailment, etc.

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This is an old story.

We' re talking about years ago before anyone heard of asbestos having any questionable properties.

detaildetail

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

[2 {conflict 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?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/Eventualitysimilardissimilargeneral-specificset-memberwhole-partexamplerestatementcomparisonattribution-contentmeans-purposecomment-topic

Instance/Typepurposeconditionalunconditional

Semantics/Pragmaticsenablementinference

Temporal Projectioncircumstancebefore-afteruntilsimultaneous

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.

[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].

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Semantics/Pragmaticsenablement

[{-enables Since [here’s coffee]}, it’s possible that [you drink it].]

[1Here’s coffee.] [{-enables So1} drink it].The presence of coffee provides the precondition for the imperative.

enablesenableshere’s coffeehere’s coffee drink it.drink it.dialog actdialog act

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

prop. contentprop. 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, equivalent, definition

Attribution: contentBackground: background, circumstanceComparison: similar, proportionComplement: supplementAdditive: conjunction, additionManner: manner

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

causalpositive

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

negativeConcession: conflictCondition: otherwise, unconditional, compromise

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Relation Naming ConventionSubject 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, mannerCollective adjective or noun is

symmetric relation.equivalent, similar, conjunction,

disjunction, contrast, conflictObject of preposition or conjunction is

$2.after, letAlone

This is not only about discourse relations but about any relations. 33

Documents

ISO/TC37/SC4/WG2 WD24617-5 SemAF - Discourse Structure 2011-01-12, Oxford HASIDA Koiti [email protected] AIST, Japan