Phrasal Translation and Query Expansion Techniques for Cross-Language Information Retrieval
- 格式:pdf
- 大小:74.92 KB
- 文档页数:8
PhrasalTranslationandQueryExpansionTechniquesforCross-LanguageInformation
Retrieval
LisaBallesterosandW.BruceCroft
balleste@cs.umass.edu,croft@cs.umass.edu
CenterforIntelligentInformationRetrieval
ComputerScienceDepartment
UniversityofMassachusetts
Amherst,MA01003-4610USA
Dictionarymethodsforcross-languageinformationretrieval
giveperformancebelowthatformono-lingualretrieval.
Failuretotranslatemulti-termphraseshasbeenshownto
beoneofthefactorsresponsiblefortheerrorsassociated
withdictionarymethods.First,westudytheimportanceof
phrasaltranslationforthisapproach.Second,weexplorethe
roleofphrasesinqueryexpansionvialocalcontextanalysis
andlocalfeedbackandshowhowtheycanbeusedtosignif-
icantlyreducetheerrorassociatedwithautomaticdictionary
translation.
ThedevelopmentofIRsystemsforlanguagesotherthan
Englishhasfocusedonbuildingmono-lingualsystems.In-
creasedavailabilityofon-linetextinlanguagesotherthan
Englishandincreasedmulti-nationalcollaborationhave
motivatedresearchincross-languageinformationretrieval
(CLIR)-thedevelopmentofsystemstoperformretrieval
acrosslanguages.
TherehavebeenthreemainapproachestoCLIR:transla-
tionviamachinetranslationtechniques[Rad94];parallelor
comparablecorpora-basedmethods[DD95a,LL90,SB96],
anddictionary-basedmethods[Sal72,Pev72,HG96,BC96].
Eachoftheseapproacheshasshownpromise,butalsohas
disadvantagesassociatedwithit.Resultssuggestthatim-
provementsgainedviamachinetranslationtechniquesmay
notoutweighthecostoflinguisticanalysis.Onedisadvan-
tageofmethodsbasedontheuseofparallelandaligned
corporaislackofresources:parallelcorporaarenotal-
waysreadilyavailableandthosethatareavailabletendto
berelativelysmallortocoveronlyasmallnumberofsub-
jects.Performanceisalsodependentonhowwellthecor-poraarealigned.Ourworktakesthethirdapproachand
appliesdictionary-basedmethods.
Automaticmachinereadabledictionary(MRD)query
translationleadstoadropineffectivenessof40-60%below
thatofmono-lingualretrieval[HG96,BC96].Thisisdue
primarilytothreefactors.First,specializedvocabularynot
containedinthedictionarywillnotbetranslated.Second,
dictionarytranslationsareinherentlyambiguousandaddex-
traneoustermstothequery.Third,failuretotranslatemulti-
termconceptsasphrasesreduceseffectiveness.
Wearedevelopingstrategiesforreducingtheerrorsas-
sociatedwithdictionary-basedmethodsandfocusonstrate-
gieswhichhavealowprocessingcostanddonotrequire
scarceresources.Thispaperexplorestheidentificationof
phrasesinqueriesandtheeffectivenessofsimplephrasal
translation.Inaddition,weinvestigatetheroleofphrasesin
queryexpansionbycomparingtwoapproaches,localfeed-
back[AF77]andLocalContextAnalysis[XC96],toex-
pandingqueriesatvariousstagesofthe“translation”pro-
cess.
Effectivesystemsformono-lingualinformationretrieval
havebeenavailableforseveralyears.Typically,research
intheareaofmulti-lingualinformationretrievalhasfocused
onincorporatingnewlanguagesintoexistingsystemstoal-
lowthemtoruninseveralmono-languageretrievalmodes.
Recently,greaterinterestinretrievalacrosslanguageshas
motivatedmoreworktostudythefactorsinvolvedinbuild-
ingaCLIRsystem.
Salton[Sal72]showedearlyonthatwithcarefullycon-
structedthesauri,cross-languageretrievalwasnearlyasef-
fectiveasmono-lingualretrieval.Thisstudywasgood,how-
everthetestcollectionwasverysmallbycurrentstandards
anditisunrealistictomanuallyindexlargerdatabases.
LandauerandLittman[LL90]havealsoproposeda
methodforcross-languageretrieval.LatentSemanticIndex-
ing(LSI)[FDD88]wasusedtocreateamultidimensional
indexingspaceforaparallelcorpusofEnglishdocuments
andtheirFrenchtranslations.Theirmethodhasbeensuc-cessfulatthetaskofretrievingaquery’stranslation,inre-
sponsetothatquery.Howeverthecollectionusedwassmall,
containing2482paragraph-lengthdocumentsfromCana-
dianParliamentaryproceedingsandnoresultsofitseffec-
tivenessonthetraditionalretrievaltaskhavebeenreported.
Themethodalsoreliesontheuseofparallelcorporawhich
arenotalwaysreadilyavailable.
Anothermethodthatreliesonparallelandalignedcor-
porahasbeensuggestedbyDunningandDavis[DD93].
Theirmethodisbasedonthevectorspacemodelandin-
volvesthelineartransformationoftherepresentationofa
queryinonelanguagetoitscorrespondingrepresentationin
anotherlanguage.Thetransformationisdonebyreduction
ofthedocumentspacetogenerateatranslationmatrix.They
havehadsomesuccessinefficientlyestimatingthetrans-
lationmatrixandresultsofteststoestimateitsqualityare
promising.Furthertestsoftheeffectivenessofthemethod
havebeenlimitedbyitscomputationalcomplexity.
DavisandDunning[DD95a,DD95b]havealsodevel-
opedseveralotherapproachestoquerytranslation,which
theytestedontheTRECISMSpanishqueriesandcollec-
tion.TwooftheserelyontheuseofaSpanish-English
parallelcorpusandoneusesevolutionaryprogrammingfor
queryoptimization.Inthefirstoftheparallelcorpusap-