Wordnet and word similarity Lectures 11 and 12.ppt

Wordnet and word similarity Lectures 11 and 12 Centrality measures (for hw2) How representative is a sentence of the overall content of a document The more similar are sentence is to the document, the more representative it is Lexical semantics: meaning of individual words Intro to Lexical Semantics Polysemy, Synonymy,… Online resources: WordNet Computational Lexical Semantics Word Sense Disambiguation Supervised Semi-supervised Word Similarity Thesaurus-based Distributional What’s a word? Definitions we’ve used: Types, tokens, stems, inflected forms, etc... Lexeme: An entry in a lexicon consisting of a pairing of a form with a single meaning representation A lemma or citation form is the grammatical form that is used to represent a lexeme. Carpet is the lemma for carpets The lemma bank has two senses: Instead, a bank can hold the investments in a custodial account in the client’s name But as agriculture burgeons on the east bank, the river will shrink even more. A sense is a discrete representation of one aspect of the meaning of a word Relationships between word meanings Polysemy Homonymy Synonymy Antonymy Hypernomy Hyponomy Homonymy Lexemes that share a form Phonological, orthographic or both But have unrelated, distinct meanings Examples bat (wooden stick-like thing) vs bat (flying scary mammal thing) bank (financial institution) versus bank (riverside) Can be homophones, homographs, or both: Homophones: Write and right Piece and peace Homonymy causes problems for NLP applications Text-to-Speech Same orthographic form but different phonological form bass vs bass Information retrieval Different meanings same orthographic form QUERY: bat care Machine Translation Speech recognition Why? Polysemy The bank is constructed from red brickI withdrew the money from the bank Are those the same sense? Which sense of bank is this? Is it distinct from (homonymous with) the river bank sense? How about the savings bank sense? Poly