Computational linguistics

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The study of natural language, as done by computer programs. Typically, this means a program trying to understand English (or French, or any other natural language) typed or spoken by a person. This field is also known as Natural Language Processing (NLP), a term that emphasizes the engineering aspect of computational linguistics.

Examples of NLP systems include computer programs that automatically

  • translate text from Japanese to English (machine translation)
  • answer a plain English question with succinct information extracted from large collections of documents
  • summarize a newspaper article

There are several problems in getting programs to understand natural language. Many of these are due to the ambiguity in the language:

  • word boundary detection: in spoken language, there are no gaps between words; where to place the word boundary often depends on what choice makes the most sense gramatically and given the context.
  • word sense disambiguation: the same word can have several different meanings; we have to select the meaning which makes the most sense in context
  • syntactic ambiguity: the grammar for natural languages is not unambiguous, i.e. there are often multiple possible parse trees for a given sentence. choosing the correct one requires semantic information
  • speech acts and plans: sentences often don't mean what they literally mean; for instance the correct answer to "can you pass the salt?" is to pass the salt, not say "yes". or again, if a class was not offered last year, the correct answer to the question "how many students failed the class last year?" is "the class was not offered last year", not "none".

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The Association for Computational Linguistics definition:

computational linguistics is the scientific study of language from a computational perspective. Computational linguists are interested in providing computational models of various kinds of linguistic phenomena.