word sense disambiguation and information retrieval ppt and ppt on word sense disambiguation
Word Meaning and
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
duermes dormirDan Jurafsky
Lemmas have senses
• One lemma “bank” can have many meanings:
• …a bank can hold the investments in a custodial account…
• “…as agriculture burgeons on the east bank the river will shrink
• Sense (or word sense)
• A discrete representation
of an aspect of a word’s meaning.
• The lemma bank here has two sensesDan Jurafsky
Homonyms: words that share a form but have
unrelated, distinct meanings:
• bank : financial institution, bank : sloping land
• bat : club for hitting a ball, bat : nocturnal flying mammal
1. Homographs (bank/bank, bat/bat)
1. Write and right
2. Piece and peaceDan Jurafsky
Homonymy causes problems for NLP
• Information retrieval
• “bat care”
• Machine Translation
• bat: murciélago (animal) or bate (for baseball)
• bass (stringed instrument) vs. bass (fish)Dan Jurafsky
• 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
• 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
• Two lexemes are synonyms
• if they can be substituted for each other in all situations
• If so they have the same propositional meaningDan Jurafsky
• 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.
• Water/H 0
• 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.
• big has a sense that means being older, or grown up
• large lacks this senseDan Jurafsky
• 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
• The class denoted by the superordinate extensionally includes the class
denoted by the hyponym
• 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
Word Senses and
Word RelationsWord Meaning and
WordNet and other
Online ThesauriDan Jurafsky
Applications of Thesauri and Ontologies
• Information Extraction
• Information Retrieval
• Question Answering
• Bioinformatics and Medical Informatics
• Machine TranslationDan Jurafsky
• 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
Adverb 4,481Dan Jurafsky
Senses of “bass” in Wordnet