Encyclopedia of Database Systems

Living Edition
| Editors: Ling Liu, M. Tamer Özsu

N-Gram Models

  • Djoerd Hiemstra
Living reference work entry
DOI: https://doi.org/10.1007/978-1-4899-7993-3_935-2

Definition

In language modeling, n-gram models are probabilistic models of text that use some limited amount of history, or word dependencies, where n refers to the number of words that participate in the dependence relation.

Key Points

In automatic speech recognition, n-grams are important to model some of the structural usage of natural language, i.e., the model uses word dependencies to assign a higher probability to “how are you today” than to “are how today you,” although both phrases contain the exact same words. If used in information retrieval, simple unigram language models ( n-gram models with n = 1), i.e., models that do not use term dependencies, result in good quality retrieval in many studies. The use of bigram models ( n-gram models with n = 2) would allow the system to model direct term dependencies, and treat the occurrence of “New York” differently from separate occurrences of “New” and “York,” possibly improving retrieval performance. The use of trigram models would...
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Recommended Reading

  1. 1.
    Metzler D, Bruce Croft W. A Markov random field model for term dependencies. In Proceedings of 31st Annual international ACM SIGIR conference on research and development in information retrieval. 2005. p. 472–9.Google Scholar
  2. 2.
    Miller DRH, Leek T, Schwartz RM. A hidden Markov model information retrieval system. In Proceedings of 22nd Annual international ACM SIGIR conference on research and development in information retrieval. 1999. p. 214–21.Google Scholar
  3. 3.
    Song F, Bruce Croft W. A general language model for information retrieval. In Proceedings of 22nd Annual international ACM SIGIR conference on research and development in information retrieval. 1999. p. 4–9.Google Scholar

Copyright information

© Springer Science+Business Media LLC 2016

Authors and Affiliations

  1. 1.University of TwenteEnschedeThe Netherlands