Structured lexicons and Lexical semantics Especially WordNet ® See D Jurafsky & JH Martin: Speech and Language Processing, Upper Saddle River NJ (2000): Prentice Hall, Chapter 16. and http://en.wikipedia.org/wiki/WordNet and explore WordNet: http://wordnet.princeton.edu/
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Structured lexiconsand Lexical semantics
Especially WordNet®
See D Jurafsky & JH Martin: Speech and Language Processing, Upper Saddle River NJ (2000): Prentice Hall, Chapter 16.
and http://en.wikipedia.org/wiki/WordNetand explore WordNet: http://wordnet.princeton.edu/
2/27
Structured lexicons• Alternative to alphabetical dictionary• List of words grouped according to meaning• Classic example Roget’s Thesaurus• Hierarchical organization is important• Hierarchies familiar as taxonomies, eg in natural
sciences– Daughters are “types of” and share certain properties,
inherited from the mother• Similar idea for ordinary words: hyponymy and
Lexical semantics• How are word meanings represented in WordNet?
– synsets (synonym sets) as basic units– a word ‘meaning’ is represented by simply listing the word forms
that can be used to express it• example: senses of board
– a piece of lumber vs. a group of people assembled for some purpose
– synsets as unambiguous designators:– {board, plank, ...} vs. {board, committee, ...}
• Members of synsets are rarely true synonyms– WordNet does not attempt to capture subtle distinctions among
members of the synset– may be due to specific details, or simply connotation, collocation
9/27
Synsets
• synsets often sufficient for differential purposes
• Synsets are linked by semantic relations, word forms are linked by lexical relations..
• Preferable for cardinality of synset to be >1– WordNet also gives a gloss for each word
meaning, and (often) an example
10/27
11/27
16.2 WORDNET: A Database of Lexical Relations
• WordNet:– The most well-developed and widely used
lexical DB for English– Handcrafting from scratch, rather than
mining information from existing dictionaries and thesauri
– Consisting three separate DBs:• One each for nouns and verbs, and• A third for adjectives and adverbs
12/27
16.2 WORDNET: A Database of Lexical Relations
Scope of current WordNet 1.6 release in terms of unique entries and total numbers of senses for the four databases.
16.2 WORDNET: A Database of Lexical Relations
A portion of the WordNet 1.6 entry for the noun bass
14/27
Lexical relations in WordNet
• WordNet is organized by semantic relations.– It is characteristic of semantic relations that they are
reciprocated– if there is a semantic relation R between meaning {x1,
x2, ...} and meaning {y1, y2, ...}, then there is a relation R between {y1,y2, ...} and {x1, x2, ...}
– Individual relations may or may not be• Symmetric R(A,B) R(B,A) (eg synonymy, not hyponymy)• Transitive R(A,B) & R(B,C) R(A,C) (eg synonymy may be)• Reflexive R(A,A) is true (synonymy is, antonymy isn’t)
15/27
Lexical relations• Nouns
– Synonym ~ antonym (opposite of)– Hypernyms (is a kind of) ~ hyponym (for example)– Holonym (is part of) ~ meronym (has as part)