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Encyclopedia of Database Systems pp 1Cite as

Null Values

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Definition

Null values are used to represent uncertain data values in a database instance.

Key Points

Since the beginning of the relational data model, null values have been investigated, with the intention of capturing and representing data values that are uncertain. Depending on the intuitions and cases of uncertainty, different kinds of null values have been proposed, e.g., they may represent information that is withheld, inapplicable, missing, unknown, etc. Thus, in principle, it could be possible to find in a hypothetical database diverse classes of null values, and also several null values of the same class. However, in commercial relational DBMSs and in the SQL Standard, only a single constant, NULL, is used to represent the missing values.

Many semantic problems appear when null values are integrated with the rest of the relational data model, which essentially follows the semantics of predicate logic. Among them, (i) the interpretation of nulls values (for a particular...

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Recommended Reading

  1. Grahne G. The Problem of incomplete information in relational databases. LNCS 554. Secaucus: Springer; 1991.

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  2. Levene M, Loizou G. A guided tour of relational databases and beyond, Chapter 5. London: Springer; 1999.

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  3. Van der Meyden R. Logical approaches to incomplete information: a survey. In: Chomicki J, Saake G, editors. Logics for databases and information systems. Boston: Kluwer; 1998. p. 307–56.

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Author information

Authors and Affiliations

  1. Carleton University, Ottawa, ON, Canada

    Leopoldo Bertossi

Authors
  1. Leopoldo Bertossi
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Corresponding author

Correspondence to Leopoldo Bertossi .

Editor information

Editors and Affiliations

  1. Georgia Institute of Technology College of Computing, Atlanta, Georgia, USA

    Ling Liu

  2. University of Waterloo School of Computer Science, Waterloo, Ontario, Canada

    M. Tamer Özsu

Section Editor information

  1. School of Informatics, University of Edinburgh, Crichton Street, EH8 9LE, Edinburgh, Scotland, UK

    Leonid Libkin

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© 2016 Springer Science+Business Media LLC

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Bertossi, L. (2016). Null Values. In: Liu, L., Özsu, M. (eds) Encyclopedia of Database Systems. Springer, New York, NY. https://doi.org/10.1007/978-1-4899-7993-3_1267-2

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  • DOI: https://doi.org/10.1007/978-1-4899-7993-3_1267-2

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  • Publisher Name: Springer, New York, NY

  • Online ISBN: 978-1-4899-7993-3

  • eBook Packages: Springer Reference Computer SciencesReference Module Computer Science and Engineering

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