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Journal of Intelligent Information Systems

, Volume 30, Issue 2, pp 93–114 | Cite as

Null values in fuzzy databases

  • Guy de TréEmail author
  • Rita de Caluwe
  • Henri Prade
Article

Abstract

Since in the real world, it often occurs that information is missing, database systems clearly need some facilities to deal with missing data. With respect to traditional database systems, the most commonly adopted approach to this problem is based on null values and three valued logic. This paper deals with the semantics and the use of null values in fuzzy databases. In dealing with missing information a distinction is made between incompleteness due to unavailability and incompleteness due to inapplicability. Both the database modelling and database querying aspects are described. With respect to attribute values, incompleteness due to unavailability is modelled by possibility distributions, which is a commonly used technique in the fuzzy databases. Domain specific null values, represented by a bottom symbol, are used to model incompleteness due to inapplicability. Extended possibilistic truth values are used to formalize the impact of data manipulation and (flexible) querying operations in the presence of these null values. The different cases of appearances of null values in the handling of selection conditions of flexible database queries are described in detail.

Keywords

Null value Incomplete information Unknown information Inapplicable information Extended possibilistic truth values Fuzzy database modelling 

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Copyright information

© Springer Science+Business Media, LLC 2006

Authors and Affiliations

  1. 1.Computer Science Laboratory, Dept. of Telecommunications and Information ProcessingGhent UniversityGentBelgium
  2. 2.Institut de Recherche en Informatique de Toulouse (IRIT)-CNRSUniversité Paul SabatierToulouse CedexFrance

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