Transactions of the Association for Computational Linguistics, vol. 6, pp. 225–240, 2018. Action Editor: Philipp Koehn.
Submission batch: 10/2017; Revision batch: 2/2018; Published 4/2018.
2018 Association for Computational Linguistics. Distributed under a CC-BY 4.0 Licence.
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ScheduledMulti-TaskLearning:FromSyntaxtoTranslationEliyahuKiperwasser∗ComputerScienceDepartmentBar-IlanUniversityRamat-Gan,Israelelikip@gmail.comMiguelBallesterosIBMResearch1101KitchawanRoad,Route134YorktownHeights,NY10598.U.Smiguel.ballesteros@ibm.comAbstractNeuralencoder-decodermodelsofmachinetranslationhaveachievedimpressiveresults,whilelearninglinguisticknowledgeofboththesourceandtargetlanguagesinanimplicitend-to-endmanner.Weproposeaframeworkinwhichourmodelbeginslearningsyntaxandtranslationinterleaved,graduallyputtingmorefocusontranslation.Usingthisapproach,weachieveconsiderableimprovementsintermsofBLEUscoreonrelativelylargeparallelcor-pus(WMT14EnglishtoGerman)andalow-resource(WITGermantoEnglish)setup.1IntroductionNeuralMachineTranslation(NMT)(KalchbrennerandBlunsom,2013;Sutskeveretal.,2014;Bah-danauetal.,2014)hasrecentlybecomethestate-of-the-artapproachtomachinetranslation(Bojaretal.,2016).Oneofthemainadvantagesofneuralap-proachesistheimpressiveabilityofRNNstoactasfeatureextractorsovertheentireinput(KiperwasserandGoldberg,2016),ratherthanfocusingonlocalinformation.Neuralarchitecturesareabletoextractlinguisticpropertiesfromtheinputsentenceintheformofmorphology(Belinkovetal.,2017)orsyn-tax(Linzenetal.,2016).Néanmoins,asshowninDyeretal.(2016)andDyer(2017),systemsthatignoreexplicitlinguis-ticstructuresareincorrectlybiasedandtheytendtomakeoverlystronglinguisticgeneralizations.Pro-vidingexplicitlinguisticinformation(Dyeretal.,∗WorkcarriedoutduringsummerinternshipatIBMRe-search.2016;Kuncoroetal.,2017;NiehuesandCho,2017;SennrichandHaddow,2016;Eriguchietal.,2017;AharoniandGoldberg,2017;Nadejdeetal.,2017;Bastingsetal.,2017;Matthewsetal.,2018)hasproventobebeneficial,achievinghigherresultsinlanguagemodelingandmachinetranslation.Multi-tasklearning(MTL)consistsofbeingabletosolvesynergistictaskswithasinglemodelbyjointlytrainingmultipletasksthatlookalike.Thefi-naldenserepresentationsoftheneuralarchitecturesencodethedifferentobjectives,andtheyleveragetheinformationfromeachtasktohelptheothers.Forexample,taskslikemultiwordexpressionde-tectionandpart-of-speechtagginghavebeenfoundveryusefulforotherslikecombinatorycategoricalgrammar(CCG)parsing,chunkingandsuper-sensetagging(BingelandSøgaard,2017).Inordertoperformaccuratetranslations,wepro-ceedbyanalogytohumans.Itisdesirabletoacquireadeepunderstandingofthelanguages;et,oncethisisacquireditispossibletolearnhowtotranslategraduallyandwithexperience(includingrevisitingandre-learningsomeaspectsofthelanguages).Weproposeasimilarstrategybyintroducingthecon-ceptofScheduledMulti-TaskLearning(Section4)inwhichweproposetointerleavethedifferenttasks.Inthispaper,weproposetolearnthestructureoflanguage(throughsyntacticparsingandpart-of-speechtagging)withamulti-tasklearningstrategywiththeintentionsofimprovingtheperformanceoftaskslikemachinetranslationthatusethatstructureandmakegeneralizations.WeachieveconsiderableimprovementsintermsofBLEUscoreonarela-tivelylargeparallelcorpus(WMT14EnglishtoGer-
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man)andalow-resource(WITGermantoEnglish)setup.Ourdifferentschedulingstrategiesshowin-terestingdifferencesinperformancebothinthelow-resourceandstandardsetups.2SequencetoSequencewithAttentionNeuralMachineTranslation(NMT)(Sutskeveretal.,2014;Bahdanauetal.,2014)directlymodelstheconditionalprobabilityp(oui|X)ofthetargetse-quenceofwordsy=
