Encyclopedia of Database Systems

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

Safety and Domain Independence

  • Rodney ToporEmail author
Reference work entry
DOI: https://doi.org/10.1007/978-1-4614-8265-9_1255




The values in the relations of a relational database are elements of one or more underlying sets called domains. In practical applications, a domain may be infinite, e.g., the set of natural numbers. In this case, the value of a relational calculus query when applied to such a database may be infinite, e.g., {n| n ≥ 10}. A query Q is called finite if the value of Q when applied to any database is finite.

Even when the database domains are finite, all that is normally known about them is that they are some finite superset of the values that occur in the database. In this case, the value of a relational calculus query may depend on such an unknown domain, e.g., {x ∣ ∀ yR(x, y)}. A query Q is called domain independent if the value of Q when applied to any database is the same for any two domains containing the database values or, equivalently, if the value of Q when applied to a database contains only values that occur in the database.

The term safequery...

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Copyright information

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

Authors and Affiliations

  1. 1.Griffith UniversityNathanAustralia

Section editors and affiliations

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