Encyclopedia of Database Systems

2018 Edition
| Editors: Ling Liu, M. Tamer Özsu

Incomplete Information

  • Gösta Grahne
Reference work entry
DOI: https://doi.org/10.1007/978-1-4614-8265-9_1241

Synonyms

Indefinite information; Null values; Uncertain information

Definition

Incomplete information arises in relational databases, when a fact (tuple) has to be inserted in a relation, and values for some required columns are missing. For instance, in an employee database, the phone number of one employee might be missing, as might the address of another employee. There are numerous reasons for such missing information, e.g., the insertion was done through a view, or the incomplete tuple originated from another database that does not record these fields. In information integration and data exchange systems incomplete information is rampant. Note that here the null values only represent unknown, existing values. The other main case, namely the one that the column heading is not applicable to the tuple in question, is not covered here, for a treatment, see e.g., [17].

It is easy to storemissing or incomplete information, by simply using a symbol, say ⊥, different from the symbols of...
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Copyright information

© Springer Science+Business Media, LLC, part of Springer Nature 2018

Authors and Affiliations

  1. 1.Concordia UniversityMontrealCanada

Section editors and affiliations

  • Leonid Libkin
    • 1
  1. 1.School of InformaticsUniversity of EdinburghEdinburghUK