Reference Resolution And Cognitive Grammar

Reference Resolution And

Cognitive Grammar

Susanne Salmon-AltLaurent Romary

Loria - Nancy, France

ICCS-01 San Sebastian, May 2001

General context

Computational objectives Designing man-machine dialogue systems with graphical user

feedback and gestural designation– Allowing the user to express himself spontaneously

Linguistic objectives Deriving a model that widely covers the range of possible

referring expressions and their use in context– Narrowing the discrepancy between computational models and

linguistic descriptions

Can a cognitive model be a means to achieve this?

Reference Resolution

Referring expressions

Contextmodel

“World”: perception and gestures

Interpretation

?

Evolution of the context

Take a big circle.

Okay, and now put a small lineon the left.

Don’t stick it to the circle.hearer puts a circle

on the screen...hearer puts a line

on the screen...


Associate referring expressions to identifying representations for contextual objects

C1 C2

C3


Take a big circle.

Okay, and now put a small lineon the left.

Don’t stick it to the circle.

{L2}

{C1} {L2}

{C1}

Referring expression Context model Referents

L1

L2 L3

The general background

Observations: reference in task-oriented dialogues – A wide variety of referring expressions: indefinites, definites,

demonstratives, pronouns– Both anaphoric and deictic uses

Modeling work is generally reduced to pronoun resolution– E.g. Centering (Grosz et al., 1995), Mitkov (1998)

Specificity of anaphoric expressions?– DRT / S-DRT: no essential difference between pronouns and

definites (linking as the main mechanism) How to integrate demonstratives (+gestures)?

Reference = Linking ?

Current strategies are basically co-referential– if indefinite : introduce a new discourse referent– if anaphoric : filter the context model on semantic

constraints and choose a suitable referent

Problems– empirically inappropriate for definites (Poesio &Vieira,

1998)– need of some additional mechanisms for...

Difficulties with Linking

Bridging

Take a triangle. Color the base in blue

one-anaphora

The green block supports the big pyramid, but not the red/small one.

ordinals andother-expressions

Take two lines. Move one line to the left.

Delete the other line.

visual information

Delete the triangle.

Need of cognitive structures rather than (or in complement to) of discourse variables

Cognitive Grammar (1)

Theoretical foundations (Langacker 1986, 1991)– language not self-contained, but part of cognitive

processing– speaker’s knowledge : inventory of symbolic units

(phonological and semantic pole)– semantic structures characterized relative to

presupposed « cognitive domains » (concepts, perceptual experiences, knowledge systems)


Semantic structure of nouns

roof

Abstract schema:Delimitation of a region

in some domain

Instantiation:Profiling a sub-structure of one (ore more) presupposed domains

knife NOUN


tr lm

horizontal

[ ON THE LEFT OF] [ THE LINE ON THE LEFT OF THE CIRCLE ]

Meaning (not truth-conditional): assembly and profiling of semantic units

Atemporal relation Assembly and profiling

[ LINE ] [ CIRCLE ]

Suitability

Interesting properties : interpretation of NPs– not linking, but profiling within a given domain

=> encompasses all kind of anaphoric expressions

– conceptual domains not primarily linguistic constructs => reference to percepual entities, gestures

– meaning = imposing a profile on a domain => prediction of preferred referential access :

The green block supports the big pyramid, but not the red/small one.

Problem : formalisation

The Model — Overview

abstract schema

for determiners

abstractschema

for nouns

complex schema for noun phrases

selected domain

restructured domain

context model

(domains)

Assembly of abstract schemas

Search for a suitable conceptual domain

Profiling of a regionof the domain

Calculus of an underspecified

domain

Unification with adomain of the context

model

Focusing an itemof a partition of the

domain

The Context Model (1)

Basic units : domains

@T1

Type = TRIANGLECard = 1Properties = {(size: big)}

@F1

Type = FIGURECard = 2Properties = {(size: small)}

Diff-Crit = Type

CIRCLE LINE

@C1 @L1

@C1

Type = CIRCLECard = 1

@L1

Type =LINECard = 1

The Context Model (2)

@F1

Type = FIGURECard = 2Properties = {(size: small)}

Diff-Crit = Type

CIRCLE LINE

@C1

@C1

Type = CIRCLECard = 1

@L1

Type =LINECard = 1

THE LINE ON THE LEFT OF THE CIRCLE

@L1

Grouping– Triggers

co-ordination prepositions argument structure perceptual criteria

– Result partitioned domain common type differentiation criterion focus structure

N

Underspecified Domains (1)

abstract schema

for determiners

abstractschema

for nouns

complex schema for noun phrases

Determiner semantics: grounding (how to locate the

thing within the given domain)

Noun semantics: delineate an item of a partitioned domain

Indefinite NPs « a N » (a line)

Noun semantics: delineate an item of type N within a domain

Determiner semantics: the item is located within a

domain of elements of type N

N N

Type = N

N


abstractschema

for nouns

abstract schema

for determiners complex

schema for noun phrases




Definite NPs « the N » (the line)

Noun semantics: delineate an item of type N within a domain

Determiner semantics: the item is located within a

domain of elements of a super-type of N

¬N ¬ N

Type > N


abstractschema

for nouns

abstract schema

for determiners complex

schema for noun phrases




Pronouns“it”

Pronoun semantics: delineate an item of a partitioned domain

Determiner semantics: Ø (the item has to be located from its focal position

focus)

Type = ?

Restructuration (1)

underspecified domain

selected domain

restructured domain

context model

(domains)

Profiling of a region in the domain

Focusing one item of the partition

Type = N

N N NN N N

Type = N

Indefinites « a N »

Restructuration (2)


selected domain

restructured domain

context model

(domains)


Focusing item N of the partition

Type > N

N ¬ N ¬NN ¬N ¬N

Type > N

Definites “the N”

Restructuration (3)


selected domain

restructured domain

context model

(domains)


No change

Type= ?

Pronouns « it »

Type = ?

Application - Example

Take a big circle.Okay, and now put a small line on the left.Don’t stick it to the circle.

Type = CIRCLEProp = BIG

@C

C4C3C2C1

Type = LINEProp = SMALL

@L

L4L3L2L1

Type = CIRCLE

@ ?

...

a big circle

Type = LINE

@ ?

...

a small line


@C

C4C3C2C1


@C1


@L

L4L3L2L1


@L1

Type = FIGURECD = TypeCD = Position

@C&L

C1 L1

Type = ?

@ ?

...

it

Type = FIGURECD = Type

@C&L

CIRCLE ¬CIR.

the circle

Discussion

Single mechanism for different kinds of reference– not linking, but extraction

bridging, one-anaphora, other-expressions integrated treatment of demonstratives (cf. full paper) takes into account visual information (required for dialogues)

Formalization of Cognitive Grammar– Implementation into a real dialogue platform– Partial validation on a corpus of human dialogues

other-expressions

– Being even for formal Expressing the constraints in the framework of S-DRT

Documents

Reference Resolution And Cognitive Grammar