Download Introduction to Part of Speech Tagging

IntroductiontoPartof
SpeechTagging
AlanRitter
ManyslidesadaptedfromBrendanO’Connor ChrisManning
Wherearewegoingwiththis?
• Textclassification:bagsofwords
• Sequencetagging
• PartsofSpeech
• NamedEntityRecognition
• Otherareas:bioinformatics(geneprediction),etc…
What’sapart-of-speech(POS)?
• Syntax=howwordscomposetoformlargermeaningbearingunits
• POS=syntacticcategoriesforwords
• Youcouldsubstitutewordswithinaclassandhaveasyntacticallyvalid
sentence
• Givesinformationhowwordscombineintolargerphrases
• Isawthedog
• Isawthecat
• Isawthe___
PartsofSpeechisanoldidea
• PerhapsstartingwithAristotleintheWest(384–322BCE),therewas
theideaofhavingpartsofspeech
• Schoolgrammar:noun,verb,adjective,adverb,preposition,
conjunction,pronoun,interjection
• Manymorefinegrainedpossibilities
https://www.youtube.com/watch?v=ODGA7ssL-6g&index=1&list=PL6795522EAD6CE2F7
Open class (lexical) words
Nouns
Proper
IBM
Italy
Verbs
Common
cat / cats
snow
Closed class (functional)
Determiners the some
Conjunctions and or
Pronouns
he its
Main
see
registered
Adjectives
old older oldest
Adverbs
slowly
Numbers
… more
122,312
one
Modals
can
had
Prepositions to with
Particles
off up
Interjections Ow Eh
… more
Openvs.Closedclasses
• Openvs.Closedclasses
• Closed:
• determiners:a,an,the
• pronouns:she,he,I
• prepositions:on,under,over,near,by,…
• Why“closed”?
• Open:
• Nouns,Verbs,Adjectives,Adverbs.
ManyTaggingStandards
• PennTreebank(45tags)…thisisthemostcommonone
• Browncorpus(85tags)
• Coarsetagsets
• UniversalPOStags(Petrovet.al.https://github.com/slavpetrov/universalpos-tags)
• Motivation:cross-linguisticregularities
Whatarepartsofspeechusefulfor?
• Phraseidentification(chunking)
• Namedentityrecognition
• InformationExtraction
• Parsing
QuickandDirtyNounPhraseIdentification
POSTagging
• WordsoftenhavemorethanonePOS:back
•
•
•
•
Theback door =JJ
Onmyback =NN
Winthevotersback =RB
Promisedtoback thebill =VB
• ThePOStaggingproblemistodeterminethePOStagforaparticular
instanceofaword.
POSTagging
• Input: Playswellwithothers
• Ambiguity:NNS/VBZUH/JJ/NN/RBINNNS
• Output: Plays/VBZwell/RBwith/INothers/NNS
• Uses:
•
•
•
•
Penn
Treebank
POStags
Text-to-speech(howdowepronounce“lead”?)
Canwriteregexps like(Det)Adj*N+overtheoutputforphrases,etc.
Asinputtoortospeedupafullparser
Ifyouknowthetag,youcanbackofftoitinothertasks
POStaggingperformance
• Howmanytagsarecorrect?(Tagaccuracy)
• About97%currently
• Butbaselineisalready90%
• Baselineisperformanceofstupidestpossiblemethod
• Tageverywordwithitsmostfrequent tag
• Tagunknown wordsasnouns
• Partlyeasybecause
• Manywordsareunambiguous
• Yougetpointsforthem(the,a,etc.)andforpunctuationmarks!
Decidingonthecorrectpartofspeechcanbe
difficultevenforpeople
• Mrs/NNPShaefer/NNPnever/RBgot/VBDaround/RP to/TO
joining/VBG
• All/DTwe/PRPgotta/VBNdo/VBis/VBZgo/VBaround/INthe/DT
corner/NN
• Chateau/NNPPetrus/NNPcosts/VBZaround/RB250/CD
HowdifficultisPOStagging?
• About11%ofthewordtypesintheBrowncorpusareambiguous
withregardtopartofspeech
• Buttheytendtobeverycommonwords.E.g.,that
• Iknowthat heishonest=IN
• Yes,that playwasnice=DT
• Youcan’tgothat far=RB
• 40%ofthewordtokensareambiguous
It’shardforpeopletoo!