f-structures, information structure, and discourse structure

LFG Winter school July 2004

PARC

F-Structures, Information Structure, and Discourse

StructureTracy H. King Annie Zaenen

PARC


PARC

Talk Outline

• Information Structure: Syntax of discourse functions

• Applications: Anaphora resolution• Discourse structure• Applications: Summarization and

Sentence Condensation• Conclusions


PARC

Information Structure: Syntax of discourse functions

• Basic discourse functions

• Typology of encoding• LFG approaches


PARC

Basic discourse functions

• DFs encode and divide up the information structure of the sentence.

• DFs are notoriously difficult to define– Topic/Theme/Given– Focus/Rheme/New– Contrastiveness

• What to do with non-DF information, e.g. background information?


PARC

Example: Clefts

• It is the [box]Focus [that]Topic I opened.• Construction encodes focus of the clefted

constituent.• The referent of that constituent is the topic

of the subordinate clause.• The ‘relative clause’ material is

‘presupposed’.

• Question-answer pairs are often used to determine DFs. – What did you open? It was the box that I opened.


PARC

Basic discourse functions

• Here focus on:– how to encode these – what they can be used for

• Choice of relevant DFs depends on what they are needed for.


PARC

Typology of encoding

• Structural position– initial– preverbal

• Discourse markers/particles• Intonation• Combinations of these


PARC

Structural encoding

• Position indicates discourse function.• Language specific

– Topics are initial– Focus are pre/post verbal– Background information is postverbal– Constructions: clefts

• Subject as default topic• LFG: designated c-structure position


PARC

Initial topics• Object marker on the verb

– Anaphoric agreement– The OM is the object

• Chichewa (Bresnan & Mchombo 1987)Alenje zi-ná-wá-lu-ma njuchi.hunters SM-past-OM-bite-indic bees`The bees bit them, the hunters.'


PARC

Preverbal focus

• Turkish (Enc 1991)bu kitab-i Hasan ban-a ver-dirthis book-acc Hasan I-dat give`This book Hasan gave to ME.'


PARC

DF markers

• Morphemes can mark DF– Japanese wa– Hindi (Sharma 2003)

• hI exclusive contrastive focus (only)• bhI inclusive contrastive focus (also)• tO contrastive topic


PARC

Hindi exampleExclusive focus:rAdha=ne=hI baccho=kO kahAnI sunAyIRadha=erg=Foc children=ACC story hear`It was (only) Radha who told the children a story'

Contrastive topic:mOmbattI=tO milI, kEkin abh mAchis gum gayEcandle=Top found but now match lost go`The candle was found but not the matches are lost.'


PARC

Intonation• Most DFs have a specific intonation

associated with them• Intonation alone can signal a DF

Did you see Mary or John? I saw JOHN.

It was a RED hat that I wore.


PARC

Combinations• Most positionally and marker-signaled

DFs also have intonation marking.• Can combine position and marker

– ay inversion in Tagalog (Kroeger 1993) ay marker as head of I SpecIP is Topic=Subj or Focus=non-Subj

– Ni lapis ay hindi nagdala si=Rosa even pencil AY not bring

nom=Rosa `Even a pencil Rosa didn't bring.'


PARC

LFG approaches

• Syntax-DF interactions• F-structure vs. I-structure• OT-LFG


PARC

Syntax-DF interactions

• Subcategorized DFs– Predicates can subcategorize for DFs.

• C-structure annotations– C-structure nodes can be associated

with DFs, similar to GF assignment in configurational languages.


PARC

Subcategorized DFs

• Malay Topic (Alsagoff 1992)– verb affix identifies Topic and equates

it with a GF• meng- ( TOP)=( SUBJ)• di- (i) ( TOP)=( SUBJ) (ii) < ( SUBJ) ( OBL) > log obj log subj• 0- ( TOP)=( OBJ)


PARC

Malay exampleMiriam MENG-cubit doktor ituMiriam MENG-pinch doctor the`Miriam pinched the doctor.'

MENG-cubit (PRED)='pinch< ( SUBJ), ( OBJ)> ( TOP)'

PRED 'pinch< ( SUBJ), ( OBJ)> ( TOP)'SUBJ [ PRED 'Miriam' ]TOP [ ]OBJ [ PRED 'doctor' ]


PARC

Chichewa and Tagalog topic

Chichewa: Bresnan & Mchombo 1987

S

NP( TOPIC)=

VP

TOPIC [ …]SUBJ [ PRED 'pro' ]PRED 'X<SUBJ,…>'

anaphoric binding

Tagalog:Kroeger 1993

CP

NP( TOPIC)=

C'


PARC

Urdu preverbal focus

VP

XP( FOCUS)=

V'

Urdu: Butt & King 1996


PARC

C- to F-structure Mapping proposal

• Clause-Prominence of DFs: DF adjuncts (i.e., in adjoined positions) must be clause-prominent, occurring either at an edge of the clause or adjacent to the head of the clause. (Bresnan 2001:192)

XP

XP

XP

YPDF

ZPAdjunct


PARC

Mapping proposal

• Specifiers of functional categories are the grammatical discourse functions (Topic, Focus, Subj). (Bresnan 2001:102)

FP

F'SpecFPDF


PARC

Intonation• Much work is done on this association

– Steedman (2000) on Categorial Grammar

• Less in LFG– Bengali and the syntax-prosody mapping

(Butt and King 1998)– Russian clause-final focus (King 1995)– Integration of prosody into the LFG

projection architecture needs more exploration.


PARC

Discourse markers

• Constructive case/morphology approach (Sharma 2003)– hI (FOC )

X(P)

X(P) Cl-disc(FOC )hI


PARC

F-structure vs. I-structure

• DFs are often represented in the f-structure.– Malay subcategorizes for Topics– Chichewa incorporated pronouns

• Scope of DFs may conflict with that of GFs.– project DFs into an I(nformation)-

structure


PARC

DF-GF mismatches

VP focus: Mary [F ate the cake].

F-structure

PRED 'eat<SUBJ,OBJ>SUBJ [ PRED 'Mary' ]OBJ [ PRED 'cake' ]TNS past

How can the focus be represented?Form I-structure constituents.


PARC

OT-LFG approaches

• OT constraints for encoding of DFs (Choi 1999)– [New]-X: Place [+New] in a salient position

X– [Prom]-X: Place [+Prom] in a salient

position X

• Languages – rank these constraints – define possible instantiations of X


PARC

Summary: Syntax of DFs• DFs can be encoded by:

– structural position– morphological markers– intonation

• Linguistic theories need a way to capture these interactions– Much LFG work on structural position and

morphological markers– Are F and T the only elements worth

distinguishing?– Need more work on integrating generalizations

about intonation– Need more work on how syntactic distinctions

relate to semantic and pragmatic concepts


PARC

Form and function relation• A radical proposal:

– Prince: the relation between syntax and pragmatics is as arbitrary as that between sound and word meaning

• Cross language variation: • e.g. functions of Left-dislocation in Yiddish and English are

different (Prince)• Functions of clefting and topicalization are different across

Germanic languages• Functions of Left-Dislocations (or Contrastive topicalization)

and Right dislocations in Romance languages and in Germanic are different (see e.g. Lambrecht 1981 on Spoken French).

• Not a one-to-one correspondence between form and function


PARC

Talk Outline


• Applications: Anaphora resolution

• Discourse structure• Applications: Summarization and



PARC

Applications for Discourse Functions

Anaphora resolution– DFs determine saliency– Saliency partially determines

resolution


PARC

Anaphora Resolution

• Have a sentence with pronouns or referring NPs (the president)

• Want to know what they refer to– some restrictions are purely syntactic: (most) reflexives refer to Subjects– others are heuristic: prefer closer referents prefer high saliency referents


PARC

Role of Discourse Functions

• Topic, and topic shift, are relevant for anaphora

• Centering theory and its variants– have an ordered list of salient

elements– have a referring expression– first salient element to match

features is the antecedent– update the list based on this


PARC

Anaphora resolution example

Brennan drives an AR. Brennan =Old, AR=NewShe drives too fast. She=Brennan=OldFriedman races her on weekends.

Friedman=Old, Brennan=Old, Her=Brennan=OldShe drives to Laguna Seca. She=Friedman=OldShe often beats her. She=Friedman=Old Her=Brennan=Old

Discourse functions determine correct anaphora resolution.


PARC

Pro-Drop and Anaphora Resolution

• Pro-drop is (partly) licensed by DFs– Already established topics are more

likely to be pro-dropped

• Centering theory:– Continue and Smooth-shift transition

favor null subjects– Chinese (Song 2003)– Yiddish (Prince 1998)


PARC

Summary: Anaphora resolution

• DFs are essential for determining anaphora resolution

• Pro-drop is licensed in part by IS• But a lot remains to be worked out.


PARC

Talk Outline


• Applications: Anaphora Resolution• Discourse structure• Applications: Summarization and



PARC

Discourse Structure

•A simple model

•Its relation to syntax


PARC

A too simple idea

S S S

D

S S


PARC

Progression and elaboration

• Joan got up early. She showered. Then she made some tea. …

• Mary is a model professor. Last year she wrote ten papers. She also advised 20 doctoral students and she was a member of the Committee on Women in Science.


PARC

A still very simple ideaD

S S D S S

S S

Discourse progresses sentence by sentence

or

Subparts elaborate on previous parts


PARC

One type of discourse trees (Linguistic Discourse

Model)John fell. Bill pushed him.

a b

S

Bill pushed John. He fell.

a b

C

a and b are BDUs (Basic Discourse Unit)

A BDU basically corresponds to a segment with an event variable in its semantics.


PARC

BDU Relations

• Not all types of relations can be classified as belonging to the subordinating or the coordinating type.– We will ignore the rest here.

• Some elements in a sentence can explicitly indicate what type of relation we have, e.g. ‘because’ is a subordination relation.– They will be called “operator segments.”


PARC

How do discourse trees relate to sentence syntax

trees?• Some textual elements guide the

discourse tree construction.

• A BDU is not necessarily a complete sentence or vice versa.


PARC

Sentence does NOT equal BDU

[The man dove into the pool.]a [It was warm and

soothing]b and [he decided to remain for a little

longer than usual.]c

a b c

S

C


PARC

ADJUNCT clauses

[Joan left]a because [she was tired.]b

Three segments: Two BDUs and 1 operator

a b

S


PARC

Textual elements that guide the construction of discourse

trees

• Hypothesis 1: Subordinating conjunctions indicate discourse subordination. – Needs checking: it is often true but is

it always true?


PARC

Textual elements cont.• Hypothesis 2: tense and aspect

– John dove into the pool. The water was warm and soothing.

– John Smith was wearing a long coat. It looked brand new.

• Stative predicates do not push the discourse forward and often indicate subordination.

• English is not very rich in this type of indicator.– perfective/imperfective distinctions are more explicit in other languages (e.g. French). (e.g. Asher and Lascarides, 2003)


PARC

Textual elements cont.

• Hypothesis 3: pronominalization– John Smith was wearing a long coat. It looked

brand new.Often the ‘promotion’ of (the referent of) an OBJ or a OBL to a SUBJ in the following sentence reflects a discourse subordination. (Polanyi et al. 2004)

• But– John hit Bill. He fell.

The tense and aspect information takes precedence.


PARC

What is the role of Information Structure in the construction of

Discourse trees?• [John Smith]T1 was wearing [a long coat]F1. [It]T2 looked brand new.

Focus-1 -->Topic-2• [John]T1 likes [sweets]F1. [He]T2 eats [three dishes of ice cream]F2 and [five chocolate bars]F2 every day .

Topic-1 --> Topic-2(cf. centering theory ‘shifts’)

In Discourse Structure both are subordinations


PARC

Are Information Structure and Discourse structure

independent?• Information structure: what the

sentence/discourse is about• Discourse structure: how we talk

about what we are talking about: – narratives– explanations– …


PARC

Where to look for a link?‘The first Christian mission to New Zealand,…., was launched by Samuel Marsden on behalf of the Church of England’s Church Missionary Society (CMS) in 1814. …Marsden, a bluff Yorshireman with ‘heavy shoulders and a face of a petulant ox’, was both chaplain to the New South Wales penal settlement and a magistrate. He was severe in dealing with convicts… But he went out of his way to meet and greet Maori in Sidney, and often… He had even, in 1809, rescued the Maori sailor Ruatara, who was stranded in London, and taken him back with him to Sidney. It was this association in particular that led Marsden to set up the first CMS mission at Rangihoua in the Bay of Islands in 1814, on land that he would buy from Ruatara.’


PARC

• The cleft seems to indicate a ‘pop’ from the subordinated material to the resumption of main narrative.

• Note also that the material in the that-clause might be presupposed in the logical sense but it is not old information (see Collins for ample examples)

• No claim that this is the only discourse structure function of it-clefts.

• No one-to-one relation, multifactorial analysis necessary.


PARC

Summary: Discourse Structure

• Discourse structure looks at how clauses and sentences are related to one another.

• Textual elements provide information on how to build up the structure but they do not completely determine it.


PARC

Talk Outline





PARC

Summarization and sentence condensation

• Summarization• Condensation


PARC

Sentence Condensation and Summarization

• Have a long text• Want a short "condensed" version

– retain most salient features– maintain grammaticality

• Choose salient sentences via Discourse structure

• Condense those sentences


PARC

Example of Discourse-driven summarization

• Our group is developing new techniques for helping manage information for enhanced collaboration. We explore solutions for seamlessly connecting people to their personal and shared resources. Our solutions include services for contextual and proactive information access, personalized and collaborative office applications, collaborative annotation and symbolic, statistical and hybrid processing of natural language. Our team includes researchers with diverse backgrounds including: ubiquitous computing, computer-supported collaboration, HCI, IR, and NLP.


PARC

Discourse Tree

A coordination of two subtrees that have subordinated elements with again coordinated or subordinated elements

C

S S

SS

ba

eS

gfc d


PARC

Discourse Structure• [Our group is developing new techniques]a for

[helping manage information for enhanced collaboration.]b [We explore solutions for seamlessly connecting people to their personal and shared resources.]c [Our solutions include services for contextual and proactive information access, personalized and collaborative office applications, collaborative annotation and symbolic, statistical and hybrid processing of natural language.]d [Our team includes researchers with diverse backgrounds]e [including:]f [ubiquitous computing, computer-supported collaboration, HCI, IR, and NLP.]g


PARC

Possible condensations• [Our group is developing new

techniques]a for [helping manage information for enhanced collaboration.]b [We explore solutions for seamlessly connecting people to their personal and shared resources.]c [Our team includes researchers with diverse backgrounds]e [including:]f [ubiquitous computing, computer-supported collaboration, HCI, IR, and NLP.]g


PARC

Possible condensations• [Our group is developing new

techniques]a for [helping manage information for enhanced collaboration.]b [Our team includes researchers with diverse backgrounds]e


PARC

Possible condensations[Our group is developing new

techniques]a [Our team includes researchers with diverse backgrounds]e


PARC

Summarization and Discourse structure

• Discourse structure allows only ‘big chunks’ to be deleted.

• We need also finer-grained structure for sentence condensation.


PARC

Role of information structure in sentence condensation

• Salient information will be discourse prominent– retain Focus– retain Topic, possibly in reduced form (e.g.

pronoun)– delete background, non-prominent

• Salient information tends to correspond to the heads of arguments in main clauses but there are a lot of special cases– ADJUNCTs can be deleted but one should

keep negations


PARC

Sentence condensation• [Our group is developing new

techniques]a for [helping manage information for enhanced collaboration.]b [We explore solutions for seamlessly connecting people to their personal and shared resources.]c

• Transfer rules dictate which f-structure parts can be deleted

X (Y ADJUNCT) &(X ADJ-TYPE) neg: X 0.


PARC

Basic Sent. Cond. system

Source XLEParsing

Target Packed F-structures

XLEGeneration

Packed Condens.Transfer

n b

est

PargramEnglish

Condensationrules

Log-linearmodel

Stochastic Selection


PARC

Summary: Summarization and Condensation

• Discourse structure can guide summarization

• F-structures are easily manipulated for condensation– F-structure distinctions give broad guidance

(ADJUNCT and MOD vs. GFs and DFs)– But there are distinctions that are important for

condensation that are very minor in the f-structure, e.g. difference between negative and other ADJUNCTS.

– Is it possible to be more systematic or is this just a reflection of the way things are?


PARC

Talk Outline





PARC

Summary

• Information-structure: sentence internal partition of the information according to discourse functions

• Discourse-structure: inter-clausal relations between successive utterances

• Both are crucial in certain applications– anaphora resolution– summarization/condensation


PARC

Conclusions

• For applications it is necessary to get all the modules worked out

• This crucially involves many aspects of linguistic theory

• The projection architecture of LFG should be helpful but a lot of work remains to be done.


PARC

References• Alsagoff, L. 1992. Topic in Malay: the Other Subject.

PhD thesis, Stanford University.• Asher, N. and A. Lascarides (2003) Logics of

Conversation, Cambrdige University Press.• Bresnan, J. 2001. Lexical-Functional Syntax.

Blackwell.• Bresnan, J. and S. Mchombo. 1987. Topic, pronoun,

and agreement in Chichewa. Linguistic Inquiry.• Butt, M. and T.H. King. 1998. Interfacing

phonology with LFG. In LFG98 Proceedings. CSLI On-line Publications.

• Choi, H.-W. 1999. Optimizing Structure in Context: Scrambling and Information Structure. CSLI Publications.


PARC

References• Collins, Peter. 1991. Cleft and pseudo-cleft

constructions in English. London and New York: Routledge.

• Enc, M. 1991. The semantics of specificity. Linguistic Inquiry.

• King, T.H. 1995. Configuring Topic and Focus in Russian. CSLI Publications.

• Kroeger, P. 1993. Phrase Structure and Grammatical Relations in Tagalog. CSLI Publications.

• Lambrecht, Knud. 1981. Topic, antitopic and verb agreement in non-standard French. Benjamins

• Polanyi, L. et al. 2004. A Rule Based Approach to Discourse Parsing, ACL Workshop

• Polanyi, L. et al. 2004. Sentential Structure and Discourse Parsing. ACL Workshop


PARC

References• Prince, Ellen, 1998. On the limits of syntax, with

reference to Left-Dislocation and Topicalization. In Culicover, P. and McNally, L., eds. The limits of syntax. NY: Academic Press.

• Prince, Ellen. 1998. Subject-Prodrop in Yiddish. In Focus: Linguistics, cognitive, and computational perspectives.

• Sharma, D. 2003. Discourse clitics and constructive morphology in Hindi. In M. Butt and T.H. King (ed) Nominals: Inside and Out. CSLI Publications.

• Song, Zhiyi. 2003. A Comparative Study of Subject Pro-drop in Old Chinese and Modern Chinese. NWAVE 32.

• Steedman, M. 2000. Information Structure and the Syntax-Phonology Interface. Linguistic Inquiry.


PARC


PARC

Example: Sentential Subjects

• [That john is an idiot]top[e-subj is obvious]sentence

f-structures, information structure, and discourse structure

Documents

discourse structuretracy

nondf information

intonationmost dfs

markersignaled dfs

storycontrastive topic

df markersmorphemes

forchoice of relevant

book hasan