WordNet

WordNet is a semantic net for the English language. It groups English words into sets of synonyms called synsets, provides short definitions, and records the various semantic relations between these synonym sets. The purpose is twofold: to produce a combination of dictionary and thesaurus that is more intuitively usable, and to support automatic text analysis and artificial intelligence applications. The database and software tools have been released under a BSD style licence and can be downloaded and used freely. The database can also be browsed online.

WordNet was created and is being maintained at the Cognitive Science Laboratory of Princeton University under the direction of psychology professor George A. Miller. Development began in 1985. Over the years, the project received about $3 million of funding, mainly from government agencies interested in machine translation.

Database contents

As of 2003, the database contains about 140,000 words organized in over 110,000 synsets for a total of 195,000 word-sense pairs; in compressed form, it is about 12 megabytes large.

WordNet distinguishes between nouns, verbs, adjectives and adverbs on the assumption that these are stored differently in the human brain. Every synset contains a group of synonymous words or collocations (a collocation is a sequence of words that go together to form a specific meaning, such as "car pool"); words typically participate in several synsets. The meaning of the synsets is further clarified with short definining glosses. A typical example synset with gloss is

good, right, ripe -- (most suitable or right for a particular purpose; "a good time to plant tomatoes"; "the right time to act"; "the time is ripe for great sociological changes")

Every synset is connected to other synsets via a number of relations. These relation vary based on the type of word:

• Nouns
  • synonyms: synsets with similar meaning
  • hypernyms: Y is a hypernym of X if every X is a (kind of) Y
  • hyponyms: Y is a hyponym of X if every Y is a (kind of) X
  • coordinate terms: Y is a coordinate term of X if X and Y share a hypernym
  • holonym: Y is a holonym of X if X is a part of Y
  • meronym: Y is a meronym of X if Y is a part of X
• Verbs
  • synonyms
  • hypernym: the noun Y is a hypernym of the verb X if the activity X is a (kind of) Y
  • coordinate terms: those verbs sharing a common hypernym
• Adjectives
  • synonyms and related nouns
  • antonyms: adjectives of opposite meaning
• Adverbs
  • synonyms and root adjectives
  • antonyms

WordNet also provides the polysemy count of a word: the number of synsets that contain the word. If a word participates in several synsets (i.e. has several senses), then typically some senses are much more common than others. WordNet quantifies this by the frequency score: in several sample texts all words were semantically tagged with the corresponding synset, and then it was counted how often a word appeared in a specific sense.

The database's interface is able to deduce the root form of a word from the user's input; only the root form is stored in the database.

Limitations

Unlike other dictionaries, WordNet does not include information about etymology, pronunciation and the forms of irregular verbs and contains only limited information about usage.

The actual lexicographical and semantical information is maintained in lexicographer files, which are then processed by a tool called grind to produce the distributed database. Neither grind nor the lexicographer files are freely available, which makes modifying and maintaining the database for outsiders quite difficult.

Related projects

The project EuroWordNet has produced WordNets for several European languages and linked them together; these are not freely available however. The Global Wordnet[?] project attempts to coordinate the production and linking of wordnets for all languages. The publishers of the Oxford English Dictionary have voiced plans to produce their own online WordNet.

The eXtended WordNet is a project at the University of Texas at Dallas which aims to improve WordNet by semantically parsing the glosses, thus making the information contained in these definitions available for automatic knowledge processing systems. It is also freely available under a license similar to WordNet's.

The GCIDE[?] project produces a dictionary by combining a public domain Webster dictionary from 1913 with some WordNet definitions and material provided by volunteers. It is released under the copyleft license GPL.

The hypernym/hyponym relationships among the noun synsets can be used as an ontology in the computer science sense. The SUMO upper ontology has produced a mapping from the WordNet synsets for nouns and verbs to SUMO classes. The OpenCyc upper ontology is also linked to WordNet. WordNet was the primary source for constructing the lower classes of the SENSUS[?] ontology.

See also:

• Semantic Web

External links:

• The WordNet Home Page (http://www.cogsci.princeton.edu/~wn/)
• Global Wordnet (http://www.globalwordnet.org/)
• EXtended WordNet (http://xwn.hlt.utdallas.edu/)
• Article about Miller and WordNet in the Star Ledger, January 22, 2002 (http://www.nj.com/news/ledger/index.ssf?/news/stories/0122wordnet)