Reference Resolution And Cognitive Grammar Susanne Salmon-Alt Laurent 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 Context model World: perception and gestures Interpretation ? Evolution of the context Take a big circle. Okay, and now put a small line on the left. Dont stick it to the circle. hearer puts a circle on the screen... hearer puts a line on the screen...

Reference Resolution Associate referring expressions to identifying representations for contextual objects C1 C2 C3 Reference Resolution Take a big circle. Okay, and now put a small line on the left. Dont stick it to the circle. {L2} {C1} {L2} {C1} Referring expressionContext modelReferents 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 and other-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 –speakers knowledge : inventory of symbolic units (phonological and semantic pole) –semantic structures characterized relative to presupposed « cognitive domains » (concepts, perceptual experiences, knowledge systems)

Cognitive Grammar (2) 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

Cognitive Grammar (3) 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 relationAssembly 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 abstract schema 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 region of the domain Calculus of an underspecified domain Unification with a domain of the context model Focusing an item of a partition of the domain

The Context Model (1) Basic units : Type = TRIANGLE Card = 1 Properties = {(size: Type = FIGURE Card = 2 Properties = {(size: small)} Diff-Crit = Type @C1 Type = CIRCLE Card = Type =LINE Card = 1

The Context Model Type = FIGURE Card = 2 Properties = {(size: small)} Diff-Crit = Type CIRCLE Type = CIRCLE Card = Type =LINE Card = 1 THE LINE ON THE LEFT OF THE 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 abstract schema 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 NN Type = N

N Underspecified Domains (2) abstract schema for nouns abstract schema for determiners 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 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 Type > N

Underspecified Domains (3) abstract schema for nouns abstract schema for determiners 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 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) underspecified domain selected domain restructured domain context model (domains) Profiling of a region in the domain Focusing item N of the partition Type > N N ¬ N ¬NN¬N Type > N Definites the N

Restructuration (3) underspecified domain selected domain restructured domain context model (domains) Profiling of a region in the domain No change Type= ? Pronouns « it » Type = ?

Application - Example Take a big circle. Okay, and now put a small line on the left. Dont stick it to the circle. Type = CIRCLE Prop = C4C3C2C1 Type = LINE Prop = L4L3L2L1 Type = ?... a big circle Type = ?... a small line Type = CIRCLE Prop = C4C3C2C1 Type = CIRCLE Prop = Type = LINE Prop = L4L3L2L1 Type = LINE Prop = Type = FIGURE CD = Type CD = C1L1 Type = ?... it Type = FIGURE CD = 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