Texts
AlexandraKlein
1
,BrigitteKrenn
1
,andHaraldTrost
2
1
AustrianResear hInstituteforArti ialIntelligen e(OFAI),
Freyung6/6,1010Vienna,Austria,
2
Se tionforArti ialIntelligen e,
CenterforMed.Statisti s,Informati s,andIntelligentSystems,
Medi alUniversityofVienna,
Freyung6/2,1010Vienna,Austria
Abstra t. Usually,humans have noproblem interpretingnegation in
text.For NLPsystems,thereare so far nostandardsolutions for
han-dlingnegations. ManyNLPsystemsdonotmodelnegationphenomena
anden ounterdi ulties wheneverfa tsare takenas given evenwhen
the statement is negated. Besides from negating obje tive fa ts,
nega-tionmayfulllotherfun tionsinnaturallanguage,su hasbeingpartof
arhetori al relation.Thus,anadequate interpretationof negations
re-quiresame hanismfordistinguishingthedierentfun tionsofnegation
asotherwise, the ontent ofa text annotbe analysedproperly.While
negationhasbeenextensivelystudiedinlinguisti s,itseemsthatthereis
no lassi ationofnegationfun tionswhi h anbeusedforNLP.Thus,
a orpus-basedstudywas arriedoutonGermannewspapertextsin
or-derto derivea taxonomy ofnegation fun tions fromthe pointof view
ofNLP.Fourmain ategorieshavebeenidentied:negationsrelatedto
statements,dis oursemarkers,speakerattitudesand idiomati
expres-sions.All ategoriesmayo urinthe ontextoftemporalmarkerswhi h
assignonly atransient validity to thenegated expression.The
atego-rizationservesasabaseforapattern-basednegation-pro essingmodule
whi hidentiesand lassiesnegations.
1 Introdu tion
Negationfullls variousfun tions intext. Inthefollowingpaper,wewillargue
that NLPsystems need to handle negation, e.g. by means of apre-pro essing
module:someinstan esofnegationmaybevitaltorepresentingtheunderlying
meaning of atext while negationin other ontexts maynot ontribute to the
propositional ontentofa orestatement.No lassi ationseemstobeavailable
whi h anbeusedtodeterminethe ontributionofnegatedexpressiontotextual
meaningfromthepointofviewofNLP.Thus,wehave arriedoutanempiri al
studyontheuseofnegationinGermannewspapertextsasabasefora
negation-pro essingmoduleforthedomain.Thestudyis motivated bybeneedsofNLP
automati pro essing.While thestudy has been arriedout onGerman
news-papertextsandwhiletherealizationofnegationislanguage-spe i ,weexpe t
thattheanalysisofnegationfun tionmayhavemanylanguage-independentand
domain-independentaspe ts.
Forillustrativepurposes,wewillgivesomeEnglishexamplesfromnewspaper
textsforwhatwe onsider themain fun tionsofnegation.Anobviousfun tion
is the reversal of thetruth value in astatement about an obje tivesituation.
Inthese ases,thestatementisexpli itlymarkedasfalse onsideringaspe i
situationand ontrarytotheassumedexpe tationsonthereader'spart[1,2℄.In
theexamplesenten e
Example 1. Ni klas Bendtner has nottravelledto Malaysiafor the rstpart of
Arsenal'spre-seasontourashe loses inonamove away from the lub. 3
thereistheunderlyingfa tofNi klasBendtner'stravelingtoMalaysiawith
Arsenal. The statement marks this as false, given the urrent situation, and
refutestheassumedpriorexpe tationonthereader'spartthattheso erplayer
willjointhepre-seasontour.Ifnegationisignoredinthissenten e,e.g.bya
bag-of-wordsapproa h,theextra tedfa ts onsistofNi klasBendtner'stravelingto
Malaysia,but they do not ontain the vitalinformation that a tually, Ni klas
Bendtner did not go on this journey with his teammates. Thus, Information
Extra tion appli ations need to in lude negations in a representation of the
ontentofatextifthenegationsarepartofstatements.
Negationdoesnotonlyo urin orestatementsregardingthepropositional
ontentofasenten e;itmayalsoindi ateaspeakerattitude.Inthesenten e
Example 2. MelaniePhillipsis,asyoumightexpe t,nothappy eitherattheidea
of thelikes of CooganandHughGrant taking amoral stan e. 4
the ore statement is the fa t that Coogan and Hugh Grant take amoral
stan e. But this is an embedded statement, and the negation is part of the
introdu tory segment of the senten e ontaining theinformation that Melanie
Phillipsisnothappy aboutthisidea.Sentiment/Subje tivityAnalysisorOpinion
Miningsystemswouldhavetotakeintoa ountthis informationasitrefersto
theopinionorattitude ofapersonwithrespe ttoasituation.
Negationmayalsosignaldierentrhetori alrelations.Inthesenten e
Example 3. Other in idents brea hed hispriva y butnotthe law. 5
3
guardian. o.uk, Ni klas Bendtner misses Arsenal's Asian tour as transfer
nears,Sunday10July2011,http://www.guardian. o.uk/footba ll/2 011/j ul/10 /
ni klas-bendtner-arsenal-tra nsfe r
4
guardian. o.uk,News of the World phone-ha king s andal part one,
Monday 11 July, http://www.guardian. o.uk/ne ws/bl og/2 011/j ul/11 /
news-world-ha king-s andal-live
5
guardian. o.uk, News International papers targeted Gordon Brown,
thementionedin identswerenotillegal.Inthis ase,anInformationExtra tion
systemhasto onsider andresolvethenegationasitis importanttonote that
the senten e essentially ontains twostatements: 1) thein identsbrea hed his
priva y,2) thein identsdidnotbrea hthelaw.
There is also a rhetori al relation whi h ontains negation as a dis ourse
markerwhi h ontributeslesstothepropositional ontentofthe orestatement:
Example 4. A ordingtothenewspaper,thefor esofMurdo hnotonly
attempt-ed to gain a ess to Brown's voi email but also obtained private banking and
medi al information. 6
Inthisexample, bothstatementsare positive: 1)the for esof Murdo h
at-tempted to gain a ess to Brown's voi email, 2) the for es of Murdo h also
obtainedprivatebankingandmedi alinformation.Thetwostatementsare
on-ne tedbymeansofnotonly...butalso.AnInformationExtra tionsystemshould
not onsiderthenegationifitdoesnotextra trhetori alrelations,butinstead
itshouldfo usonthetwopositivestatements.
Negationsmayalsobemodiedbytemporalmarkers:
Example 5. News International hasnot yetrespondedtothe laims. 7
Here, the negation refers to a situation at a ertain point in time, whi h
maybetransitory.Temporalmodi ationsmayinuen ealltypesofnegations.
Information Extra tionand OpinionMining systemsneedtotakeinto a ount
temporalmodierswhi hmayindi ate transientsituations.
As the examples have shown, it is important to analyse whi h parts of a
statement or its ontext are negated and what the intended ee ts are. For
theextra tion ofrelations, itisessentialto onsider negatedrelationsbetween
termsor on eptsasnegativeexpressionsareoftenmu h morethanmere
fun -tionwordsfromthepointofviewofsystemsrepresentingorannotatingtextual
ontent.
2 Handling Negation in NLP
Mostof resear h on erningNLPandnegationhasbeen arried outin the
do-mainofbiomedi altexts.Negationisimportantinthisdomainasitmayindi ate
theabsen e of ertain relevantsymptoms, pre- onditions,oradverserea tions.
This isindispensableinformationforele troni patient re ords,quality ontrol
andbillingpurposes.Inapproa hesforextra tinginformation frombiomedi al
text, negationis handled by dening or learningpatterns for ombinations of
negationmarkersandmedi al on epts, f.e.g.[3,4℄.Corporaofbiomedi altexts
6
Ameri anJournalismReview,The Es alatingMurdo hS andal,Monday11July
2011,http://www.ajr.org/Arti le.asp?i d=510 9
7
English [5℄.
In ontrast to NLP systems for biomedi al texts, resear h on Information
Extra tioninotherdomainshasjuststartedtoexaminethefun tionsandee ts
ofnegation.[6,7℄representre entapproa hestoin orporatingnegationinNLP
beyond the medi al domain. The appli ation is the dete tion of oni ts and
in onsisten iesamongpie esofinformationforautomati questionanswering.
Another eld of resear h where negation has to be onsidered is
Senti-ment/Subje tivityAnalysisandOpinionMining;foranoverview, f.[8℄.Inorder
to representnegative ontexts of opinion words,words orphrases are marked
as negative, and they are added to the features whi h are used to determine
thepositive,negativeorneutralpolarityofanexpression[9,10℄.[11℄distinguish
betweenprior and ontextualpolarityof expression whi h maybereversed by
negation. [12℄ des ribe a system for determining the s ope of negation using
ConditionalRandomField(CRFs)modelswhi haretrainedontheoutputofa
dependen yparer.
Toourknowledge,no lassi ationsofnegationfun tionsareavailablewhi h
anbeadoptedinNLPsystems.[1℄has arriedoutanempiri alstudyon orpora
ofwrittenandspokenEnglish,andshehasanalysedtheuseofnegation.Shehas
deriveda lassi ationwhereshedistinguishesbetweenthetwomain fun tions
REJECTIONandDENIAL.REJECTION on ernssuggestionswhileDENIAL
on erns propositions. This lassi ation omes from a orpus- or
dis ourse-linguisti sperspe tive;itla ks on ernfortherequirementsofNLPappli ations.
In parti ular, it does not dierentiate between negated propositional ontent,
negationinspeakerattitudes,rhetori alrelationsandidiomati expressionsand
the ontributionofnegationtotextualmeaningasanalyzedbyNLPsystems.
3 Empiri al study: Negation in a orpus of German news
texts
CorporaofGermannewspapertextsserveasbaseforouranalysis ofnegation.
Whiletherearemany onventionsregardingthestyleofnewspaperarti les,there
is a large variety of expressions ompared to other domains, and newspaper
arti les over a wide range of topi s, somedes ribing temporal developments.
Furthermore, large orpora are available not only for English, but also for
otherlanguages.Wethereforethink thatnewspaperarti lesareasuitablebase
for a lassi ation of negation fun tion beyond morelimited domains su h as
biomedi altexts.
We onsider only instan es of expli it negation and only lexi ally realized
negation.Wedidnottakeintoa ountmorphologi alnegation,e.g.en odedin
theprexun-,asinapproa heswhi harebasedonbag-of-words,awordwitha
negativeprexbe omesafeature,while lexi al negationhasto be analysedin
lexemes,e.g.deny whi hoftensignalsnegationinthebiomedi aldomain:
Example 6. The patient deniesany hest pain.
As a lexeme, deny arries a positive and a negative meaning. The a t of
stating somethingis positive, while theassertionthat something isnot trueis
negative. deny ombines both aspe ts. The rationalefor the ex lusion of any
lexemes whi harenotonlynegation'fun tionwords'liesin thefa t that,from
the point of view of NLP, lexemes with positive/negativemeaning tend to be
domain-dependent, produ tive due to wordformation pro esses, and fuzzy or
non-binaryin polarityassignment(e.g.hardly).
TheNEGRA orpus[13℄Version2isasynta ti allyannotatedGerman
or-pus ofnewspapertexts. Inorder to derive anegation sub orpus, all senten es
ontaining one or more negation elements were extra ted from the rst 4000
senten esoftheNEGRA orpus.626(15.7%)ofthe4000senten es ontain705
negation elements, with weder...no h, the Germanequivalent to neither...nor,
being ountedasonenegationelement.Mostsenten es ontainonlyonenegation
element,butthereweresenten eswithuptofournegationelements.
ni ht ('not')is themostfrequentnegationelement, whi h isnotsurprising,
as itis the main negationlexeme for senten e negation in German, similar to
theEnglishnot.Figure1showsalistofallnegationelementswhi hwerefound
in thesub orpuswiththeirfrequen yofo urren e.
Negationelement Count %
ni ht ('not') 46866.7% kein ('no') 10314.7% ohne ('without') 53 7.5% ni hts ('nothing') 23 3.3% nie ('never') 21 3.0% weder...no h ('neither...nor') 10 1.4% niemand ('nobody') 8 1.1%
keinerlei ('no...atall/no...whatsoever') 3 0.4%
niemandem ('nobody'),dat) 3 0.4%
nirgendwo ('nowhere') 2 0.3%
keineswegs('bynomeans') 2 0.3%
niemanden ('nobody',a ) 2 0.3%
keins ('none') 1 0.1%
ni ht-('non-') 1 0.1%
nirgends ('nowhere') 1 0.1%
niemals ('never') 1 0.1%
Fig.1.Negationelements
our negation-pro essingmodule to berobust, whi h pre ludes relyingon deep
parsing. On the other hand, the whole negated statement whi h is important
forrelationextra tionandontologybuildingmay onsistofmorethantheverb
phrase. Therefore, we have fo ussed on negation ontext in terms of the ore
statementswhi h ontainnegationsaswellasthestatementswhi harepartof
arhetori alrelationmodiedbynegation.
4 Classifying the Fun tion of Negation
Forabottom-up lassi ationof negationfun tions, wehave startedfrom the
senten estru ture.Analyzingthenegationsub orpus,itbe omesapparentthat
negationappearsinfourtypesofsenten estru ture:Statement,Rhetori al
Re-lation,SpeakerAttitudeandNegativePolarityItem/Idiomati Expression.
Fig-ure2showshowthe 705lexi allyrealized negationelementsappearaspartof
astatement,arhetori alrelation,aspeakerattitude, and aNPI, basedonthe
manualannotation. Type Count % Statement 58082.3 Rhetori alrelation 9012.8 Speakerattitude 29 4.1 NPI/Idiomati expression 6 0.9
Fig.2.Contextsandfun tionsofnegation
Inthefollowing,wewillbrieydes ribethefourtypesoffun tionsand
illus-tratethem with examplesfrom the orpus.All negation fun tionsmayappear
inthe ontextoftemporalinformation.Temporalmodiersweremarkedinthe
orpus.
4.1 Statement
Forthe purpose of identifying the s ope and fun tion of negation, we lassify
a statement as propositional ontent whi h may be represented in terms of a
predi ate-argumentstru ture. Astatementmay be lexi alizedasa lauseora
nounphrase.Negationinsinglestatementsmaynegatethepredi ate(averbin
averbphrase,anominalizationin aNP)oroneormoreofitsattributes.
Thefollowingsenten efromthe orpus(senten enumber35intheNEGRA
orpus),whi histakenfromareviewofa on ert,givesanexampleofanegated
statement:
Example 7. Selbst die otteren Passagen werden nie ausgelassen und fröhli h.
Negationsmaybepartofrhetori alrelations.Withinrhetori alrelations,
nega-tionsmay ontributeto thepropositional ontentof astatement,orthey may
marktherelation withoutnegatingastatement.Relations betweenstatements
establish textual oheren e. Rhetori al Stru tureTheory (RST) [14℄ and
Seg-mentedDis ourse RepresentationTheory(SDRT) [15℄relyonvarying
invento-riesofdis ourserelationsintextanalysisandgeneration.Insome ases,asubset
ofrelationsissele tedwhi hismostrelevantinaspe i appli ation.Rhetori al
relations onne tsequen esofstatements;theymaybeimpli it,orsignaledby
dis oursemarkers.
For Information Extra tion, it is importantto distinguish the ontribution
(with respe t to propositional ontent)and fun tion of negation.All instan es
of expli itnegationin thenewspapersub orpuswere examinedin orderto
de-termineiftheyo uraspartofarhetori alrelation.Theinventoryofrhetori al
relations was taken from the SDRT relations dened in [15℄. [16℄ presents an
approa hfor using linguisti uesto lassify rhetori alrelations from asubset
of the SDRT relation inventory in [15℄.In the newspaper negationsub orpus,
threedierenttypesofrhetori alrelationswereasso iatedwithnegations:
CONTRAST:
ni ht...sondern (not...but ), ni ht...aber (not...however) signal a
CON-TRASTrelation. The rst partof the sequen edes ribesastatement
(re-ferringtoanexpe tation)whi hismarkedasfalse.Inthese ond part,itis
repla edbyinformationwhi hdes ribesthea tualsituation.Bothsegments
usuallyshare some ommon featuresin form and ontent. InCONTRAST
ontexts,negationisimportantasitexpli itlyreje tsanexpe tation.
Examplefromthe orpus:
ni htdas Wort, sonderndie Tatistwi htig (2978)
(`notwords,buta tionsareimportant')
CONTINUATION:
Patternsofthetypeni htnur...sondern(notonly...butalso),signala
CON-TINUATIONrelation.These ondpartofthesequen e,whi hmay ontain
moreunexpe tedinformationthantherstpart,isaddedbymeansof
negat-ingrestri tiveadverbssu hasnur orallein(`only',`simply').In
CONTINU-ATION ontexts,thenegationonlyhasarhetori alfun tion.Its ontribution
tothe propositional ontent anbe negle ted.Forthe purposesof analysis
in anNLPsystem, thenegation andrestri tion anbe removed, and both
parts anbetreatedasrelatedfa ts withequal ontributions.
Examplefromthe orpus:
Ni htnureinTanz,sondern einGefühl (3437)
(`notonlyadan e,butafeeling')
whi hmustbegivenforonestatementinorderforase ondstatementtobe
appli able.
Examplefromthe orpus:
Allerdings soll diesnur mögli h sein, wennsi h Kunst ni ht in den Dienst
politis her Fors hrittskonzeptestellt. (1810)
(`however this should only be possible if art does not adhere to politi al
on eptsofprogress')
If negation is part of a rhetori al relation, negation marks a sequen e of
statementsand establishesarelationbetweentheminform and ontent.
4.3 Speaker attitude
Newspaper ommentary is a genre whi h ontainsa omplex mixture of fa ts
andopinions[18,17℄.Inthesub orpus,speakerattitudeswereexpressedmostly
byverbsand adje tives.If anegationo urred,itreversed themeaning ofthe
verboradje tive,e.g.
Fürni ht empfehlenswerthält erFuÿball
[
...]
(2224)(`Hedoesnotre ommend(playing)so er')
[1℄notesinherempiri alstudythatnegationtendstoo uroftenwithmental
verbssu hasthink.
4.4 NPIs/Idiomati expressions
Whilethepreviouslydes ribed ategoriesfor ategorizingnegationsemploy
fun -tional riteria,lexi alizedexpressions ontainingnegationelementswereassigned
theirown ategorysin etheseexpressionshavetoberepresentedasawholein
orderto grasptextualmeaning.These asesare importantforInformation
Ex-tra tionsystemsasbag-of-wordsapproa hesmay omeupwithdistortedresults
ifidiomati expressionaretakenliterally.Lexi al itemsmaypreferorestablish
negative ontexts.Insome ases,theresultingexpressionsareidiomati
expres-sions,e.g. He didn'tbudge.Er zu kte ni ht mit derWimper.Other examples
notbeingidiomati expressionsin thestri t sense arelexemes whi h are likely
too urwithinnegative onstru tions,e.g.any inEnglish.
In the sub orpus, only six dierent instan es of idiomati expressions
ontainingnegationo urred, f.Figure3.
ForGerman,alistofNPIsisavailable whi hhasbeenextra tedfromlarge
orporausing o-o urren einformation[19,20℄.Thislistishelpfulfor
automat-i allydete tingnegationwhenitis partofanNPI.Sin e ollo ationsarerigid
ni htKindervonTraurigkeitsein `toknowhowtoenjoyoneself' (235)
keinGeringerer als `noneotherthan' (1084)
ni hthinterdemBerghalten `tobeunhesitating' (1678)
ni hts hle htstaunen `tobeastonished' (3528)
ni htverhehlen `notto on eal' (3616)
überGeldni htreden sonderneshaben`nottotalk aboutmoneybuttohaveit'(3744)
Fig.3. NPIs/Idiomati expressions
5 Automati pattern-based analysis of negations
The analysis of negation in the NEGRA orpus, whi h was des ribed in the
previousse tions, hasresultedin agoldstandardaswellaspatterns for
nega-tionre ognitionand lassi ation.Inordertoexaminewhetherthe lassi ation
whi hwasderivedfromtheNEGRA orpus anbeappliedtoothernewstexts,a
se ond orpuswasbuiltwhi h onsistsofarti lesfromtheAustriandaily
news-paperDer Standard.65 arti lespublished on thesamedayin various se tions
of the newspaperwere sele ted. The orpuswaspro essed by apart-of-spee h
tagger[21℄,whi halsoassignedsenten eboundaries.In ontrasttothesituation
intheNEGRA orpus,bothpart-of-spee htagsandsenten eboundariesinthe
Standard orpuswere not orre tedmanually.The senten esweredivided into
segmentsa ordingtorules.Theaimwasto reatesegments onsistingofaone
statementea h. Thepatternsfornegationidenti ation and lassi ationwere
formulatedasregularexpressions,andtheywereappliedtotheStandard orpus.
Theresultsofthenegationidenti ationand lassi ationwerethen ompared
toamanualannotation.
A ording to the assignment of senten e boundaries, the orpus ontains
1611 senten es; 169 senten es (i.e. 10.5 % of the 1611 senten es) ontain at
least one negation element. The 1611 senten es in the Standard orpus were
automati ally separated into segments, yielding 4952 segments. 171 segments
(i.e. 3.45% of the segments) ontain at least onenegation element. In the171
segments, 138 ases of negated statements, 15 ases of rhetori al relations (9
for the CONDITION relation, 4 for the CONTRAST relation and 1 for the
CONTINUATIONrelation),17 asesofspeakerattitudesandonly1 aseofan
NPIwereassigned.14temporalmarkerswereidentiedbythesystem.
Allnegationelementswereidentied orre tly,whi h omesasnosurpriseas
wehave on entratedon expli itlexi alnegation, witha losed lassof lexi al
items.Of the169senten es ontainingatleastone negationelement,112(66.3
%) weresegmented orre tly,i.e.in awaythat thenegatedstatementwas
seg-mented.Intheremaining37 ases,adeepersynta ti analysisisneeded.Sin ein
ontrasttotheNEGRA orpus,theStandard orpusisrawandwasnot leaned
disam-determinewheter oordination onne tsdierentstatementsorwhether it
on-ne tsdierentelementswithinonestatement,e.g.
Example 8. Man soll jani ht überkritis h oder vorauseilendbösesein
[
...]
(`one shouldnotbeover riti alandanti ipartorilymean
[
...]
')wherethe negations opeextends to bothadje tives, but thesegmentation
separatesthematthe oordinationand versus
Example 9. Wenn ni hts passiert und die Regierung auf das Errei hen des
Nulldezits wartet
[
...]
(`ifnothinghappensandthegovernmentawaitsrea hingzerode it
[
...]
')wherethe oordinationseparatestwostatements.
TheStandard negation orpus ontainsonlyoneNPI,anditwasnotfound
bythesystemasitis not ontainedin theNPIlistforGerman[20℄. This may
beduetothefa tthatitisanexpressionwhi his ommoninAustrianGerman,
but less ommon in Standard German (S hmied vs. S hmiedl 'expert vs. non
expert').
Ofthe17instan esofspeakerattitudeswereassigned,none anbe onsidered
ana tualspeakerattitude.Thepatternsonlyapplyto aseswherethespeaker
attitude on ernedanembeddedsenten ewiththea tualstatementdes ribing
anobje tivesituation.12 ofthe lassi ationsaredue to errorsofthe
part-of-spee htagger.Thus,itturned outthat theassignmentofspeakerattitudesdid
notyieldany orre tassignmentswithouttakingintoa ountthea tualopinion
words;theintegrationoflexi alindi atorsforspeakerattitudesseemsne essary.
Forrhetori alfun tions,however,allassignmentsin theStandard negation
orpusare orre t. Insum, all15 instan es ofrhetori alfun tions were found,
namely 9for theCONDITION relation, 4for the CONTRASTrelation and1
fortheCONTINUATIONrelation.
Of the14 temporal modiers identied in theStandard negation orpus,4
indi ate `notyet'and 10indi ate `notanymore'.2ofthese assignmentsturned
out to be false positives. There are no false negatives. The errors are due to
lexi alambiguities.
6 Con lusion
Unstru turedtextsarelayeredstru tureswhi h onveyinformationaboutfa ts,
(e.g. ausal ortemporal) relationshipsandattitudes to readers.Ea h negation
elemento urring in atext playsa role in presentingthis information by
em-phasizingthat a ertain assumed fa t isnot validin agivensituation.Human
readersorlistenersareusually abletointerpretthisinformationgiventhe
on-text. They develop a representation of the positive fa ts in a statement and
reversethepolarityofthenegatedaspe tsofthestatement.Apartfromsystems
straight-fa ts, without onsidering negated ontexts. Sin e the ontribution of negated
informationtothepropositional ontentdependsonthefun tionofnegationin
aspe i ontext,dierenttypesofnegationsneedtobedistinguished.Inorder
to ome up with a lassi ation of negation fun tion, an empiri al study was
arriedout;Germannewspapertextsweresele tedasasampledomain.
Anegation sub orpus wasderivedbysele ting senten es whi h ontain
ex-pli it lexi alnegationfrom asample oftheNEGRA orpus.A lassi ationof
thefun tionsoftheobservednegationsandtheir ontextswasderived,basedon
theperspe tiveofNLPappli ationssu hasInformationExtra tionandOpinion
Mining.Negationelements,s opesandfun tionswereannotatedinthe
sub or-pus.
Asanextstep,thenegationphenomenawhi hwereen ounteredinthe
NE-GRA sub orpuswere transformed into regularexpressions for apattern-based
negation-pro essing approa h. A small raw orpus of texts from the Austrian
newspaperDer Standard waspart-of-spee h tagged,and thepatternswere
ap-pliedtothetest orpus.Theresultsareen ouraging:itturnsoutthateventhis
simpleapproa hperformsreasonablywellidentifyingfa tualnegation,rhetori al
relations and temporal modiers. Forthe lassi ation ofnegation in the
on-text of speakerattitudes, morelexi al resour esare needed. Thesegmentation
ofnegatedstatementsstillneedstobeimproved.
Fromthepointofviewoflinguisti resour es,theempiri alstudyhasresulted
inanannotatednegationsub orpusofGermannewspapertextswhi hmayprove
usefulinvariousappli ations.Furthermore,a lassi ationofnegationfun tions
wasderivedwhi hdes ribesthenegationphenomenaintheGermannewspaper
orpus but whi h also an be applied to other languages and domains. From
there,patternsdes ribingfun tionsofnegationsinGermanwere reatedwhi h
will beextended and integratedinto anegation-lteringmodule whi h an be
usedbyNLPsystemsforGerman.
A knowledgment
The Austrian Resear h Institute for Arti ial Intelligen e is supported by the
AustrianFederalMinistryforTransport,Innovation, andTe hnology.
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