Encyclopedia of Database Systems

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

Safety and Domain Independence

Living reference work entry
DOI: https://doi.org/10.1007/978-1-4899-7993-3_1255-2



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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© Springer Science+Business Media LLC 2016

Authors and Affiliations

  1. 1.Griffith UniversityNathanAustralia