Slide 1Slide 2Today’s AgendaParts of SpeechHow do we define POS?Parts of SpeechOpen Class POSNounsVerbsAdjectives and AdverbsClosed Class POSParticle vs. PrepositionsMore Closed Class POSClosed Class POS: ConjunctionsSlide 15Slide 16Slide 17Slide 18Slide 19Back to regularly scheduled programming…POS Tagging: What’s the task?Penn Treebank Tagset: 45 TagsPenn Treebank Tagset: ChoicesWhy do POS tagging?Why is it hard?Try your hand at tagging…Try your hand at tagging…Why is it hard?*Part-of-Speech TaggingIt’s all about the benjaminsEvolution of the EvaluationEvaluation MetricComponents of a Proper EvaluationPart-of-Speech TaggingAutomatic POS TaggingRule-Based POS TaggingEngCG ArchitectureEngCG: Sample Lexical EntriesEngCG: Constraint Rule ApplicationEngCG: EvaluationSupervised Machine LearningThree Laws of Machine LearningThree Pillars of Statistical NLPAutomatic POS TaggingLearn to automatically paint the next Cubist masterpieceTBL: TrainingTBL: TrainingTBL: TrainingTBL: TrainingTBL: TrainingTBL: TrainingTBL: TrainingTBL: TestingTBL: TestingTBL: TestingTBL: TestingTBL: TestingTBL: TestingTBL Painting AlgorithmTBL Painting AlgorithmTBL Painting AlgorithmTBL TemplatesTBL Example RulesTBL POS TaggingThree Pillars of Statistical NLPIn case you missed it…Penn Treebank TagsetTurkish MorphologyTurkish Morphological AnalyzerMorphology Annotation SchemeHow to tackle the problem…Learning Decision ListsResultsWhat we covered today…Part-of-Speech TaggingCMSC 723: Computational Linguistics I ― Session #4Jimmy LinThe iSchoolUniversity of MarylandWednesday, September 23, 2009Source: Calvin and HobbsToday’s AgendaWhat are parts of speech (POS)?What is POS tagging?Methods for automatic POS taggingRule-based POS taggingTransformation-based learning for POS taggingAlong the way…EvaluationSupervised machine learningParts of Speech“Equivalence class” of linguistic entities“Categories” or “types” of wordsStudy dates back to the ancient GreeksDionysius Thrax of Alexandria (c. 100 BC)8 parts of speech: noun, verb, pronoun, preposition, adverb, conjunction, participle, articleRemarkably enduring list!4How do we define POS?By meaningVerbs are actionsAdjectives are propertiesNouns are thingsBy the syntactic environmentWhat occurs nearby?What does it act as?By what morphological processes affect itWhat affixes does it take?Combination of the aboveUnreliable! Think back to the comic!Parts of SpeechOpen classImpossible to completely enumerateNew words continuously being invented, borrowed, etc.Closed classClosed, fixed membershipReasonably easy to enumerateGenerally, short function words that “structure” sentencesOpen Class POSFour major open classes in EnglishNounsVerbsAdjectivesAdverbsAll languages have nouns and verbs... but may not have the other twoNounsOpen classNew inventions all the time: muggle, webinar, ...Semantics:Generally, words for people, places, thingsBut not always (bandwidth, energy, ...)Syntactic environment:Occurring with determinersPluralizable, possessivizableOther characteristics:Mass vs. count nounsVerbsOpen classNew inventions all the time: google, tweet, ...Semantics:Generally, denote actions, processes, etc.Syntactic environment:Intransitive, transitive, ditransitiveAlternationsOther characteristics:Main vs. auxiliary verbsGerunds (verbs behaving like nouns)Participles (verbs behaving like adjectives)Adjectives and AdverbsAdjectivesGenerally modify nouns, e.g., tall girlAdverbsA semantic and formal potpourri…Sometimes modify verbs, e.g., sang beautifullySometimes modify adjectives, e.g., extremely hotClosed Class POSPrepositionsIn English, occurring before noun phrasesSpecifying some type of relation (spatial, temporal, …)Examples: on the shelf, before noonParticlesResembles a preposition, but used with a verb (“phrasal verbs”)Examples: find out, turn over, go onParticle vs. PrepositionsHe came by the office in a hurryHe came by his fortune honestlyWe ran up the phone billWe ran up the small hillHe lived down the blockHe never lived down the nicknames(by = preposition)(by = particle)(up = particle)(up = preposition)(down = preposition)(down = particle)More Closed Class POSDeterminersEstablish reference for a nounExamples: a, an, the (articles), that, this, many, such, …PronounsRefer to person or entities: he, she, itPossessive pronouns: his, her, itsWh-pronouns: what, whoClosed Class POS: ConjunctionsCoordinating conjunctionsJoin two elements of “equal status”Examples: cats and dogs, salad or soupSubordinating conjunctionsJoin two elements of “unequal status”Examples: We’ll leave after you finish eating. While I was waiting in line, I saw my friend.Complementizers are a special case: I think that you should finish your assignmentLest you think it’s an Anglo-centric world,It’s time to visit ......The (Linguistic) Twilight ZoneTurkishuygarlaştıramadıklarımızdanmışsınızcasına →uygar+laş+tır+ama+dık+lar+ımız+dan+mış+sınız+casınabehaving as if you are among those whom we could not cause to become civilizedDigressionThe (Linguistic)Twilight ZonePerhaps, not so strange…ChineseNo verb/adjective distinction!漂漂 : beautiful/to be beautifulTzeltal (Mayan language spoken in Chiapas)Only 3000 root forms in the vocabularyThe verb ‘EAT’ has eight variations:General : TUNBananas and soft stuff : LO’Beans and crunchy stuff : K’UXTortillas and bread : WE’Meat and Chilies : TI’Sugarcane : TZ’ULiquids : UCH’DigressionThe (Linguistic)Twilight ZoneRiau Indonesian/MalayNo ArticlesNo Tense Marking3rd person pronouns neutral to both gender and numberNo features distinguishing verbs from nounsDigressionThe (Linguistic)Twilight ZoneAyam (chicken) Makan (eat)The chicken is eatingThe chicken ateThe chicken will eatThe chicken is being eatenWhere the chicken is eatingHow the chicken is eatingSomebody is eating the chickenThe chicken that is eatingRiau Indonesian/MalayDigressionThe (Linguistic)Twilight ZoneBack to regularly scheduled programming…POS Tagging: What’s the task?Process of assigning part-of-speech tags to wordsBut what tags are we going to assign?Coarse grained: noun, verb, adjective, adverb, …Fine grained: {proper, common}