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Meta-level constraints for linguistic domain interaction
Philippe Blache
To cite this version:
Philippe Blache. Meta-level constraints for linguistic domain interaction. International Workshop on Parsing Technologies (IWPT), 2003, Nancy, France. pp.245-246. �hal-00244501�
linguistic domains
PhilippeBlache
LPL-CNRS, Universite de Provence
29 Avenue Robert Schuman, 13621Aix-en-Provence, France
pb@lpl.univ-aix.fr
Submission type: Short paper
Abstract
Thispaperpresentsatechniquefortherepresentationandtheimplementationofinter-
actionrelationsbetweendierentdomainsoflinguisticanalysis. Thissolutionreliesonthe
localizationofthelinguisticobjectsinthecontext. Therelationsarethenimplementedby
meansofinteractionconstraints,eachdomaininformationbeingexpressedindependently.
1 Introduction
Descriptivelinguisticsaswellasnaturallanguageprocessingarefacedwiththequestionofin-
tegrating dierentsourcesofinformation,comingfrom dierentdomainsoflinguistic analysis
such as prosody, phonology, syntax, discourse,semantics,etc. None ofthese domains canbe
treatedindependently. Moreprecisely,theinteractionbetweendomainscontainsinitselfmany
informationthatisnotaccessibledirectly. Itisthennecessarytoexplainhowsuchinteraction
is possible. Unfortunately, even if many works exist describing the interfacebetweentwo of
thesedomains(e.g. prosody/syntaxinteraction),noneofthemprovideageneralframeworkfor
(1)representingand(2)implementingsuchinteraction. Bothquestionsareequallyimportant.
Indeed, we think that themain obstaclesof theclassicalapproachescome from thefact that
relations betweendomains areclassicallyexpressed betweenhigh-levelstructures (e.g. asyn-
tactictreeand aprosodichierarchy)andthat theseapproaches(typicallythegenerativeones
in syntax)cannoteasily dealwithpartial,spreadorevenill-formedinformation.
Wepropose in this papersomeelementsof answerfor these problems in which the repre-
sentation level relies on an anchoring system allowingto localize any kind of information at
anylevel. Theinteractionitselfcanthenbeimplementeddirectlybymeansofinteractioncon-
straints. Inafullyconstraint-basedapproachastheoneproposedhere,interactionconstraints
exploit the interpretation of the state of the constraint system for each domain in order to
propagate newinformation: theyconstitute then ameta-level. This method presents several
interests. First,itconstitutesaneÆcienttoolforcontrollingtheparseofthedierentdomains
and implements directlysome disambiguationinformation (see section 4). But it also repre-
sentsarststeptowardsageneral accountof amulti-perspectivelinguisticanalysis in which
partialinformationcomingfromthese domainsandsecondontheinteraction betweenthem.
2 Domain interaction
Thequestionoftheinteractionbetweendierentcomponentsoflinguisticanalysisisgenerally
addressedintermsofrelationsbetweenstructures. Inthisperspective,itbecomesverydiÆcult
toconsidermorethantwostructuresatthesametimeandthisprobablyexplainsthatexisting
worksusuallytakeintoconsiderationonlytwocomponents(prosody/syntax,syntax/semantics,
etc.). Such approaches presents several problems. Oneis the necessity of representinginfor-
mation and rules within a unique formalism: relations depend in this case on the way of
representinginformation. Moreover,weneedforthis averyspecic architectureconsistingin
building rstthe respective structures,analyzing them, andapplying nally someinteraction
rules expressedin terms ofcorrespondence relationsbetweenthese structures. Wethink that
one of the problems comes from the choice of the interaction level between thecomponents.
It seems preferableto use alow-levelanchoringsystem that makes itpossibleto localize the
information in theinput. It becomesthen possibleto representinformation overagivenseg-
ment of the input instead of astructure. In this perspective, relations between domains are
independentfromanyformalismandrelyonthecharacterizationofsomepropertiesfromeach
domain.
Wepresentinthefollowingsomeinteractionexamplesbetweendierentdomains. [Bear90]
proposes an implementation of the interaction between prosodic breaks and syntactic con-
stituents. Theauthors observethat when alarge prosodicbreak appearsbetweentwowords,
theydonotcombinetoformaconstituentinwhichthecorrespondingcategoriesaresisters. In
otherwords,nomajorprosodicbreakcanseparatealexicalheadandajuxtaposedcomplement
whereasratherlongbreakscanappearbetweentwocomplements. Thiskindofinformationis
of greathelp duringaparseand allowsto resolvemanyambiguous attachments. Theauthors
represent this information directly in the grammar by inserting anew category, called Link,
betweeneach categoryof aright-hand sideof aphrasestructurerule. EachLink canbecon-
strainedin itspossiblevalues. Forexample,in theruleVP ! VLink PP, thebreakbetween
V and PPcannot begreaterthan 2(inascale of0-5). Itfollowsfrom this integrativerepre-
sentationtwopossibilities. Eitherwethink possibleand necessaryto representafullprosodic
descriptioncontainingotherinformationthanbreaks(such astone, accent,duration,etc.). In
thiscase,theinsertionofprosodicinformationintoPS-rulesrequiresacompletesuperposition
ofprosodicandsyntacticstructures. Thesecond possiblechoiceconsistsin consideringbreaks
assyntacticcategories. Inouropinion,theseinterpretation areequallybad.
Anotherexampleofprosody/syntaxinteractionisgivenin[Hirst93]. Theauthorproposesa
rulepredictingthepossibleintonationalphrasesfromasyntactictree. Thisruleisformulatedas
tree, where[X] is amajor category(S, NP,VP orPP)". Inthecaseofthetree: [
S [
NP Jane]
[
VP [
V gave][
NP
thebook][
PP to[
NP
Mary]]]]therulepredictsthefollowingphrasings:
1. (JanegavethebooktoMary) 4. (Jane)(gavethebook)(toMary)
2. (Janegave)(thebooktoMary) 5. (Jane)(gave)(thebook)(toMary)
3. (Janegavethebook)(toMary) 6. (Janegave)(thebook)(toMary)
Thiskindofruleisalsohighlydependentfromthestructureandmoregenerallytheformal-
ism. Inthiscase,theinformationisnotintegratedtothegrammarasinthepreviousexample,
theruleissituatedatahigherlevelwhichgivessomekindofprioritytothesyntacticstructure
whichhastobebuiltbeforeruleapplication.
Thethirdexampleillustratesalessstudiedinteractionbetweengraphicsandtexts. [Pineda00]
proposes adescription of coreferences between objects from dierent domains. The problem
consists in associating atext and amap. Several objects are described in both sources, the
questionistond thecoreferentones. This consistsforexamplein associatingapointwitha
city, a linewith a border,etc. then to resolve thereference bymeans of informationcoming
from onedomainoranother. Forexample, let'simaginealine betweentwopointsandatext
telling that Paris is to the west from Berlin. Then, it becomes possible to associate them
respectivelytotherightandtheleftpoint. [Pineda00]proposesamultimodalversionofDRT
(see [Kamp93]) in which all possiblereferents (foreach domain) are indicatedtogether with
propertiesplusaninteractionlevelspecifyingsometranslationconstraintsbetweenthedomains.
Inthis case,each domainkeepsin acertainsenseits autonomy, theinteractionisrepresented
by the fact that there is a common set of objects plus some equations unifying them. This
techniquereliesonthefactthatbothdomainsgivesinformationoversemanticobjectswhereas
in the previousexamples, informationwas given overobjectslocated at thesame position in
thesignal. However,asinthepreviouscases,interactionisdescribedintermsofsuperposition:
it is implemented by means of translation between the languageof onedomain towards the
languageoftheother.
Theseexamplesillustrateseveralproblems. Itisclearthat thedierentlinguisticdomains
interact. Butthis canonlyexceptionallybedescribedin terms ofstructure superposition (as
formorphology/phonologyinteractionasdescribedin[Bird94]). Usually,thereisacertainkind
of correspondencebetweensubparts of domain information, asdescribedin [Hirst93]. But it
seemsdiÆcult,orevenimpossible,tosystematize such anapproach inorder toimplementall
thepossibledomaininteractions.
3 Anchoring the dierent levels
An importantpartoftheproblemconsistsinndinganinterfacepointbetweendomainsmore
than an alignment between structures. As it is the case in multimodal communication, sev-
eral parameters have to be taken into account, in particular redundancy and synchronicity.
[Kettebekov02]). In some other cases, it is asynchronousbut redundant in the sense that it
refersto thesameinterpretationdomain. In bothcases,there exists acommon pointmaking
itpossibleto indicatethattwosetsofpropertiesrefertothesameobject.
Weproposetospecifyanewkindoffeaturedescribingaposition(ormoregenerallyalocal-
ization)thatcanbeassociatedtoaninformation. Thisideatorefertotheinformationbymeans
ofitslocalizationisexperimentedincorpusannotationworks(see[Bird01]or[Blache01a]). We
proposehere to dene ageneric solutionfor indexing any kindof information. Forsomedo-
mains(typicallyprosody)atemporalindexingcomesnaturallyinmind. But,asshownbefore,
it is notadequatefor alldomains. A linearindexing overthestringis forexample necessary
for indexing written material. Finally, wealso need to index information that is not usually
associatedwithagivenposition but moregenerallywith acontext. Thisis typicallythecase
fordiscourseinformation. Weproposethentouseananchorwhichisrepresentedbyacomplex
featureasfollows:
anchor 2
4 temporal
i,j
position
k,l
contextc 3
5
Thetemporalindexis representedbytwovalues(beginningandend). Theposition isalso
a coupleof indexes(corresponding to nodes in a chartinterpretation) localizing anobjectin
the input. The context feature implements the notion of universe (i.e. a set of discourse
referents)asinDRT.Anobjectcanthenbespeciedbymeansofdierentkindofinformation:
itsdomainanditscharacterization(the setofcorrespondingproperties)containingitsanchor.
Thefollowingexampledescribesanobjectfromthesyntacticdomain,withapreciselocalization
bothonthetemporal andthelinearaxis:
obj 2
6
6
6
4
domainsynt
charac 2
6
4 catDet
anchor
"
temp
880,1000
position
2,3
# 3
7
5 3
7
7
7
5
4 Meta-level constraints
Representinginteraction betweendierentlinguisticdomains requires thepossibilityof repre-
senting direct relations between the objects of these domains. But this is not suÆcient and
in most ofthecases, such interaction relationsrequiretheknowledgeofmoreinformation, in
particular the local relations that can exists between objects (e.g. function in syntax). This
kind ofmulti-levelinformation is easily accessiblewhen using aconstraint-basedapproachin
which all information, at any level, is representedby means of constraints (alsoconceivedas
properties). Wedescribeheresuch anapproach,called Property Grammars, and showhowit
candealwithdierentlevelsofconstraint.
We presentin this sectiontheformalismof Property Grammars (see [Blache00]), in which all
informationisrepresentedmymeansofconstraints. Concerningsyntax,thefollowingsetofcon-
straintscanbeused: linearity, dependency,obligation,exclusion,requirementanduniqueness 1
.
Theycanbepresentedasfollows:
Constraint Denition Example
Linearity() Linearprecedenceconstraints. DetN
Dependency(;)
Dependency relations between cate-
gories.
AP;N
Obligation(7!)
Set of compulsory and unique cate-
gories. One of these categories (and
onlyone)hastoberealizedinaphrase.
N7!NP
Exclusion(6,)
Restriction of cooccurrence between
setsofcategories.
N[pro]6,Det
Requirement())
Mandatorycooccurrencebetweensets
ofcategories.
N[com])Det
Uniqueness(Uniq)
Set ofcategories which cannot bere-
peatedinaphrase.
Uniq(NP)=fDet,N,AP,PP,Prog
Each category is described in the grammar with a set of such constraints. A grammar
correspondsthentoaconstraintsystem. Inthisapproach,analyzinganinputcomestoevaluate
theconstraintsystem. Thestateofthesystemafterevaluationcontainsforeachcategorytheset
ofconstraintstogetherwiththeirstatus(satisedornot). Thisresult(calledcharacterization)
contains all the necessaryinformation (actually more than aclassical syntacticstructure) in
orderto specifypreciselythesyntacticpropertiesof theinput.
Inthis approach, the generalparsingmechanism(see [Blache01b]) consists, startingfrom
the set of lexical categories, in identifying all the relations connecting the categories. As a
side eect, this process can instantiate new feature values as well as new categories. The
followingschemapresentsthe core of the process. It consists in evaluating for all subsets of
categories whethertheycan beevaluated withrespect totheconstraintsystem. Ifso,theset
ofevaluatedconstraintsisaddedtothecharacterizationofthecorrespondingcategoryX.This
characterizationistoitsturnaddedtotheconstraintstoreofthedomainandthenewcategory
Xis addedto theset ofcategories.
1. S=setofcategories
2. for eachS'S
3. SAT(S');X
4. ifX6=;
5. Charac(X) SAT(S')
6. Store(X) Charac(X)
7. S S[fXg
Attheendoftheprocess,weobtainasetofcategoriestogetherwiththeircharacterization.
Itis thenpossibletoexhibitone(orseveral)solutionswhichcorrespondtoatotalcoverageof
theinput. Itisimportanttonoticethatacharacterizationcancontainnon-satisedconstraints,
whichmeansthatitispossibleto characterizeanykindofinput,beingitgrammaticalornot.
1
Itcanbethecasethatotherkindofconstraintsarenecessary(e.g. thejuxtapositionrelation). Onesimply
havetoaddtherequiredconstrainttothesystemwithoutmodifyingthegeneralarchitecture.
4.2 A meta-level for the description of interaction
The descriptionof domain interaction takes advantageof the constraint-basedapproach pre-
sentedabove. Theideais toproposeamechanismmakingit possibleto infernewproperties
according to the dierent characterizations produced for dierent domains. In other words,
thisnewkindofconstraintspecies arelationbetweencharacterizations(ratherthanbetween
categories). Insofarasdierentsourcesofinformation,comingfrom dierentdomains,arein-
volvedin these relations,thecharacterizationshaveto specifythe domainand theanchor. A
rstapproximationoftheinteractionrelationcanberepresentedasfollows:
(
obj
i
"
domaind
i
h
characc
i
anchorai i
#
,...,obj
j
"
domaind
j
h
characc
j
anchoraj i
#)
) (
obj
k
"
domaind
k
h
characc
k
anchorak i
#
,...,obj
l
"
domaind
l
h
characc
l
anchoral i
#)
(1)
Sucharelationmeansthatwhenthedierentcharacterizationsfobj
i
,... obj
j
g,eventually
comingfrom dierentdomains, are exhibited, thenthenew properties stipulatedin thechar-
acterizations fobj
k
, ... obj
l
gare added to thegeneral description. Moreover, itis possible
(even necessary) to specify akind of meeting point betweenthe domains indicating that the
dierentcharacterizationsspecifythesamephenomenon. Thisisdonebymeansoftheanchor
feature. Twokind of relations canbeused in such interaction constraints: an inferenceone,
similar to the requirement relationin property grammars, and anexclusion onestipulatinga
cooccurrency restriction betweentwo characterizations. The generalschema consists now in
building characterizations of each domain and propagating new properties according to the
interaction constraints. Thispropagationis doneat thesametime asthesatisfactionprocess:
newpropertiesarepropagatedthankstointeractionassoonasthecorrespondingcharacteriza-
tionsare instantiated. Theevaluation ofthe interactionconstraintconstitutesin itselfapart
of a generalcharacterization of the input. It establishes then somerelations (requirementor
exclusion)betweencategoriesthat canhaveadisambiguationeect.
We illustrate in the following this aspect with an example of interaction constraints im-
plementing therelation described in [Bear90] and presented in the rstsection. It stipulates
that no majorbreaks canseparate twojuxtaposed sisters connectedwith acomplementation
relation(representedby;). Theanchoringinformation allowsto situateeach object. This is
themaininterestofsucharepresentation: anobjectonlyhavetobelocated,itspropertiescan
2
6
6
6
6
6
6
6
6
6
6
6
6
4 domsynt
char 2
6
6
6
6
6
6
6
6
6
6
4 2
6
4 catc
1
anch
"
temp
t
1 ,t
2
pos
i,j
# 3
7
5
2
6
4 catc2
anch
"
temp
t3,t4
pos
k,l
# 3
7
5
depc2;c1
3
7
7
7
7
7
7
7
7
7
7
5 3
7
7
7
7
7
7
7
7
7
7
7
7
5 6,
2
6
6
6
4 dompros
char 2
6
4 catbreak
anch
"
temp
t
2 ,t
3
pos
j,k
# 3
7
5 3
7
7
7
5 (2)
Thisinteractionconstraintconnectstwocharacterizationscomingfromtheprosodicandthe
syntacticdomains. Suchinteractionconstrainttypicallyworksforattachmentdisambiguation.
In caseof ambiguity (forexample in PPattachment), theinterpretation that will befavored
thankstothisconstraintistheoneatthehigherlevelwhen amajorbreakprecedesthePP.
5 Perspectives
Interaction constraintscanrepresent many dierent kind of information. In particular, they
can be generalized to the representation of multimodal relations by means of the proposed
anchoringsystem,includingtemporalandcontextualindexes. Wepresentin thissectionsome
examplesillustratingthese aspects.
Therstconstraint,implementacoreferencerelationmymeansofunication. Inthiscase,
interaction constraint is represented with a conjunction. It involves three characterizations
comingfromthreedierentdomains.
2
6
6
4
domgesture
char 2
4 deictic
anch
temp
i,j
contC
3
5 3
7
7
5
^ 2
6
6
4 domlang
char 2
4 sem
refx
anch h
temp
i,j
i 3
5 3
7
7
5
^ 2
6
4
domgraph
char
"
sem
refx
anch
contc12C
# 3
7
5 (3)
Theconstraint(3) representsa relationbetweengesture, graphics andlanguage domains,
occurringfor exampleduring weatherTVbroadcasts. Theconstraintsindicatesthat adeictic
gesture (see [Kettebekov02]), in a certain universe (noted C) at a given time, stipulates a
coreferencebetweenanobjectspeciedinthelanguagedomain(forexampleapronoun)atthe
same time position and a discourse referent from the graphical domain (for examplea map)
that belongsto theuniverseC. Thisconstraintisformalizedasaconjunction(ratherthanan
implication)indicatingacovariation,thedierentobjectdescriptionsbeingatthesamelevel.
2
6
6
6
6
4 domling
char 2
6
6
4 sem
"
refx
content h
quant9x
relweaken(x) i
#
anchor
contextc
1
3
7
7
5 3
7
7
7
7
5
^ 2
6
6
6
6
4
domgraphics
char 2
6
6
4 sem
"
refy
content h
quant9y
relstorm(x) i
#
anchor
contextc
1
3
7
7
5 3
7
7
7
7
5 ) (4)
