Word sense disambiguation ppt

word sense disambiguation and information retrieval ppt and ppt on word sense disambiguation
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Dr.DouglasPatton,United States,Teacher
Published Date:26-07-2017
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Word Meaning and Similarity Word Senses and Word RelationsDan Jurafsky Reminder: lemma and wordform • A lemma or citation form • Same stem, part of speech, rough semantics • A wordform • The “inflected” word as it appears in text Wordform Lemma banks bank sung sing duermes dormirDan Jurafsky Lemmas have senses • One lemma “bank” can have many meanings: • …a bank can hold the investments in a custodial account… Sense 1: 1 • “…as agriculture burgeons on the east bank the river will shrink even more” Sense 2: 2 • Sense (or word sense) • A discrete representation of an aspect of a word’s meaning. • The lemma bank here has two sensesDan Jurafsky Homonymy Homonyms: words that share a form but have unrelated, distinct meanings: • bank : financial institution, bank : sloping land 1 2 • bat : club for hitting a ball, bat : nocturnal flying mammal 1 2 1. Homographs (bank/bank, bat/bat) 2. Homophones: 1. Write and right 2. Piece and peaceDan Jurafsky Homonymy causes problems for NLP applications • Information retrieval • “bat care” • Machine Translation • bat: murciélago (animal) or bate (for baseball) • Text-to-Speech • bass (stringed instrument) vs. bass (fish)Dan Jurafsky Polysemy • 1. The bank was constructed in 1875 out of local red brick. • 2. I withdrew the money from the bank • Are those the same sense? • Sense 2: “A financial institution” • Sense 1: “The building belonging to a financial institution” • A polysemous word has related meanings • Most non-rare words have multiple meaningsDan Jurafsky Metonymy or Systematic Polysemy: A systematic relationship between senses • Lots of types of polysemy are systematic • School, university, hospital • All can mean the institution or the building. • A systematic relationship: • Building Organization • Other such kinds of systematic polysemy: Author (Jane Austen wrote Emma) Works of Author (I love Jane Austen) Tree (Plums have beautiful blossoms) Fruit (I ate a preserved plum)Dan Jurafsky How do we know when a word has more than one sense? • The “zeugma” test: Two senses of serve? • Which flights serve breakfast? • Does Lufthansa serve Philadelphia? • ?Does Lufthansa serve breakfast and San Jose? • Since this conjunction sounds weird, • we say that these are two different senses of “serve”Dan Jurafsky Synonyms • Word that have the same meaning in some or all contexts. • filbert / hazelnut • couch / sofa • big / large • automobile / car • vomit / throw up • Water / H 0 2 • Two lexemes are synonyms • if they can be substituted for each other in all situations • If so they have the same propositional meaningDan Jurafsky Synonyms • But there are few (or no) examples of perfect synonymy. • Even if many aspects of meaning are identical • Still may not preserve the acceptability based on notions of politeness, slang, register, genre, etc. • Example: • Water/H 0 2 • Big/large • Brave/courageousDan Jurafsky Synonymy is a relation between senses rather than words • Consider the words big and large • Are they synonyms? • How big is that plane? • Would I be flying on a large or small plane? • How about here: • Miss Nelson became a kind of big sister to Benjamin. • ?Miss Nelson became a kind of large sister to Benjamin. • Why? • big has a sense that means being older, or grown up • large lacks this senseDan Jurafsky Antonyms • Senses that are opposites with respect to one feature of meaning • Otherwise, they are very similar dark/light short/long fast/slow rise/fall hot/cold up/down in/out • More formally: antonyms can • define a binary opposition or be at opposite ends of a scale • long/short, fast/slow • Be reversives: • rise/fall, up/downDan Jurafsky Hyponymy and Hypernymy • One sense is a hyponym of another if the first sense is more specific, denoting a subclass of the other • car is a hyponym of vehicle • mango is a hyponym of fruit • Conversely hypernym/superordinate (“hyper is super”) • vehicle is a hypernym of car • fruit is a hypernym of mango Superordinate/hyper vehicle fruit furniture Subordinate/hyponym car mango chairDan Jurafsky Hyponymy more formally • Extensional: • The class denoted by the superordinate extensionally includes the class denoted by the hyponym • Entailment: • A sense A is a hyponym of sense B if being an A entails being a B • Hyponymy is usually transitive • (A hypo B and B hypo C entails A hypo C) • Another name: the IS-A hierarchy • A IS-A B (or A ISA B) • B subsumes ADan Jurafsky Hyponyms and Instances • WordNet has both classes and instances. • An instance is an individual, a proper noun that is a unique entity • San Francisco is an instance of city • But city is a class • city is a hyponym of municipality...location... 15Word Meaning and Similarity Word Senses and Word RelationsWord Meaning and Similarity WordNet and other Online ThesauriDan Jurafsky Applications of Thesauri and Ontologies • Information Extraction • Information Retrieval • Question Answering • Bioinformatics and Medical Informatics • Machine TranslationDan Jurafsky WordNet 3.0 • A hierarchically organized lexical database • On-line thesaurus + aspects of a dictionary • Some other languages available or under development • (Arabic, Finnish, German, Portuguese…) Category Unique Strings Noun 117,798 Verb 11,529 Adjective 22,479 Adverb 4,481Dan Jurafsky Senses of “bass” in Wordnet