Encyclopedia of Database Systems

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

Conditional Tables

  • Gösta Grahne
Reference work entry
DOI: https://doi.org/10.1007/978-1-4614-8265-9_1253

Synonyms

C-tables; Extended relations

Definition

A conditional table [4] generalizes relations in two ways. First, in the entries in the columns, variables, representing unknown values, are allowed in addition to the usual constants. The second generalization is that each tuple is associated with a condition, which is a Boolean combination of atoms of the form x = y, x = a, a = b, for x, y null values (variables), and a, b constants. A conditional table essentially represents an existentially quantified function free first order theory.

Formally, let con be a countably infinite set of constants, and var be a countably infinite set of variables, disjoint from con. Let U be a finite set of attributes, and RU a relational schema. A tuple in a c-table over R is a mapping from R, and a special attribute, denoted φ, to convarβ, where β is the set of all Boolean combinations of equality atoms, as above. Every attribute in R maps to a variable or a constant, and φ maps to β. In a...
This is a preview of subscription content, log in to check access.

Recommended Reading

  1. 1.
    Abiteboul S, Duschka OM. Complexity of answering queries using materialized views. In: Proceedings of the 17th ACM SIGACT-SIGMOD-SIGART Symposium on Principles of Database Systems; 1998. p. 254–63.Google Scholar
  2. 2.
    Abiteboul S, Kanellakis PC, Grahne G. On the representation and querying of sets of possible worlds. Theor Comput Sci. 1991;78(1):158–87.MathSciNetzbMATHGoogle Scholar
  3. 3.
    Grahne G, Mendelzon AO. Tableau techniques for querying information sources through global schemas. In: Proceedings of the 7th International Conference on Database Theory; 1999. p. 332–47.Google Scholar
  4. 4.
    Imielinski T, Lipski Jr W. Incomplete information in relational databases. J ACM. 1984;31(4):761–91.MathSciNetzbMATHCrossRefGoogle Scholar

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