Conditional dependencies for horizontal decompositions

  • P. De Bra
  • J. Paredaens
Conference paper
Part of the Lecture Notes in Computer Science book series (LNCS, volume 154)


A new decomposition theory for functional dependencies in the Relational Database Model is given. It uses a method to break up a relation into two subrelations whose union is the given relation. This horizontal decomposition is based on a new constraint: the conditional-functional dependency. It indicates how to decompose a relation into two restrictions of this relation. The only difference between the two subrelations is a functional dependency that holds in one subrelation but not in the other. Functional dependencies can be expressed as special conditional-functional dependencies.

The membership problem is solved for this new constraint, and also for another constraint, induced by the horizontal decomposition: the afunctional dependency.

An algorithm is described that performs the decomposition. It uses a new normal form: the Conditional Normal Form. The link between the horizontal- and the traditional vertical decomposition is explained.


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  1. [Ar]
    Armstrong W., Dependency structures of database relationships, Proc. IFIP 74, North Holland, pp. 580–583, 1974.Google Scholar
  2. [Be]
    Beeri C, Bernstein P.A., Computational Problems related to the Design of Normal Form Relation Schemes, ACM TODS, vol. 4.1, pp. 30–59, 1979.Google Scholar
  3. [Ber]
    Bernstein P.A., Normalization and Functional Dependencies in the Relational Database Model, CSRG-60, 1975.Google Scholar
  4. [Co]
    Codd E., Further normalizations of the database relational model, In Data Base Systems (R. Rustin, ed.) Prentice Hall, N.J., pp. 33–64, 1972.Google Scholar
  5. [De1]
    De Bra P., Paredaens J., The membership and the inheritance of functional and afunctional dependencies, Dept. of Math., Univ. of Antwerp, Belgium, report 81-39, 1981.Google Scholar
  6. [De2]
    De Bra P., Paredaens J., Horizontal Decompositions for Handling Exceptions to Functional Dependencies, CERT-82 workshop “Logical Bases for Data Bases”, France, 1982.Google Scholar
  7. [Fa]
    Fagin R., Armstrong Databases, IBM RJ 3440, 1982Google Scholar
  8. [Pa]
    Paredaens J., De Bra P., On Horizontal Decompositions, XP2-Congress, State Univ. of Pennsylvania, 1981.Google Scholar
  9. [Sm]
    Smith J., Smith D., Data base abstractions: Aggregation and generalization, ACM TODS, vol. 2.2, pp. 105–133, 1977.Google Scholar
  10. [Ul]
    Ullman J., Principles of Database Systems, Pitman, 1980.Google Scholar

Copyright information

© Springer-Verlag Berlin Heidelberg 1983

Authors and Affiliations

  • P. De Bra
    • 1
  • J. Paredaens
    • 1
  1. 1.Department of MathematicsUniversity of Antwerp, U.I.A.AntwerpBelgium

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