Abstract. In this paper, we propose a method for labelling prepositional phrases according to two different semantic role classifications, as contained in the Penn treebank and the CoNLL 2004 Semantic Role Labelling data set. Our results illustrate the dif

methodwithaholisticSRLsystemtodemonstratetheabilityofPPsemanticrolelabellingtoenhanceoverallsystemperformance.

SincethefocusoftheCoNLLdataisonSRLrelativetoasetofpre-determinedverbsforeachsentenceinput,4ourprimaryobjectiveistoinves-tigatewhethertheperformanceofSRLsystemsingeneralcanbeimprovedinanywaybyanindependentprepositionSRLsystem.Weachievethisbyembed-dingourPPclassi cationmethodwithinanexistingholisticSRLsystem—thatisasystemwhichattemptstotagallsemanticroletypesintheCoNLL2004data—throughthefollowingthreesteps:

1.PerformSRLoneachprepositionintheCoNLLdataset;2.MergetheoutputoftheprepositionSRLwiththeoutputofagivenverbSRLsystemoverthesamedataset;3.PerformstandardCoNLLSRLevaluationoverthemergedoutput.

ThedetailsofprepositionSRLandcombinationwiththeoutputofaholisticSRLsystemarediscussedbelow.

3.1BreakdownofthePrepositionSemanticRoleLabellingProblemPrepositionsemanticrolelabellingovertheCoNLLdatasetisconsiderablymorecomplicatedthanthetaskofdisambiguatingprepositionsemanticrolesinthePenntreebank.TherearethreeseparatesubtaskswhicharerequiredtoperformprepositionSRL:

1.VerbAttachment:determiningwhichprepositionisattachedtowhichverb.2.PrepositionSemanticRoleDisambiguation3.Segmentation:determiningtheboundariesofthesemanticroles.

Thethreesubtasksarenottotallyindependentofeachother,aswedemon-strateintheresultssection,andimprovedperformanceoveroneofthesubtasksdoesnotnecessarilycorrelatewithanimprovementinthe nalresults.

3.2VerbAttachmentClassi cation

Verbattachment(VA)classi cationisthe rststepofprepositionsemanticrolelabellingandinvolvesdeterminingtheverbattachmentsiteforagivenpreposition,i.e.whichofthepre-identi edverbsinthesentencetheprepositionisgovernedby.Normally,thistaskwouldbeperformedbyaparser.However,sincetheCoNLLdatasetcontainsnoparsinginformation5andwedidnotwanttouseanyresourcesnotexplicitlyprovidedintheCoNLLdata,wehadtoconstructaVAclassi ertospeci callyperformthistask.

Thisclassi erusesthefollowingfeatures,allofwhicharederivedfrominfor-mationprovidedintheCoNLLdata: