Definition
Let R(A 1,...,A n ) be a relation schema and Σ a set of functional dependencies over R(A 1,...,A n ). An attribute A i (i ∈{1,...,n}) is a prime attribute if A i is an element of some key of R(A 1,...,A n ). Then specification (R, Σ) is said to be in Third Normal Form (3NF) if for every nontrivial functional dependency X → A implied by Σ, it holds that X is a superkey for R or A is a prime attribute [2].
Key Points
In order to avoid update anomalies in database schemas containing functional dependencies, 3NF was introduced by Codd in [2]. This normal form is defined in terms of the notions of prime attribute and key as shown above. For example, given a relation schema R(A, B, C) and a set of functional dependencies Σ = {AB → C,C → B}, it holds that (R(A, B, C), Σ) is in 3NF since AB is a superkey and C is a prime attribute (given that AC is a key for R). On the other hand, (S(A, B, C), Γ) is not in 3NF if Γ = {A → B}, since A is not a superkey for S and Bis not a prime...
This is a preview of subscription content, log in via an institution.
Buying options
Tax calculation will be finalised at checkout
Purchases are for personal use only
Learn about institutional subscriptionsRecommended Reading
Biskup J., Dayal U., and Bernstein P. Synthesizing independent database schemas. In Proc. ACM SIGMOD Int. Conf. on Management of Data, 1979, pp. 143–151.
Codd E.F. Further normalization of the data base relational model. In Proc. Data Base Systems. Prentice-Hall, Englewood Cliffs, NJ, USA, 1972, pp. 33–64.
Jou J. and Fischer P. The complexity of recognizing 3NF relation schemes. Inf. Process. Lett., 14(4):187–190, 1982.
Author information
Authors and Affiliations
Editor information
Editors and Affiliations
Rights and permissions
Copyright information
© 2009 Springer Science+Business Media, LLC
About this entry
Cite this entry
Arenas, M. (2009). Third Normal Form. In: LIU, L., ÖZSU, M.T. (eds) Encyclopedia of Database Systems. Springer, Boston, MA. https://doi.org/10.1007/978-0-387-39940-9_1264
Download citation
DOI: https://doi.org/10.1007/978-0-387-39940-9_1264
Publisher Name: Springer, Boston, MA
Print ISBN: 978-0-387-35544-3
Online ISBN: 978-0-387-39940-9
eBook Packages: Computer ScienceReference Module Computer Science and Engineering