Synonyms
2NF
Definition
Let R(A1,…, An) be a relation schema and Σ a set of functional dependencies over R(A1,…, An). An attribute Ai (i ∈{1,…,n}) is a prime attribute if Ai is an element of some key of R(A1,…, An). Then specification (R, Σ) is said to be in second normal form (2NF) if for every nontrivial functional dependency X → A implied by Σ, it holds that A is a prime attribute or X is not a proper subset of any (candidate) key for R [1].
Key Points
In order to avoid update anomalies in database schemas containing functional dependencies, 2NF was introduced by Codd in [1]. 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 = {A → B}, it does not hold that (R(A, B, C), Σ) is in 2NF since B is not a prime attribute and A is a proper subset of the key AC. On the other hand, (S(A, B, C), Γ) is in 2NF if Γ = {A → B, B → C}, since Ais a key (and thus it...
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
Further CEF. Normalization of the data base relational model. In: Data base systems. Englewood Cliffs: Prentice-Hall; 1972. p. 33–64.
Author information
Authors and Affiliations
Corresponding author
Editor information
Editors and Affiliations
Section Editor information
Rights and permissions
Copyright information
© 2018 Springer Science+Business Media, LLC, part of Springer Nature
About this entry
Cite this entry
Arenas, M. (2018). Second Normal Form (2NF). In: Liu, L., Özsu, M.T. (eds) Encyclopedia of Database Systems. Springer, New York, NY. https://doi.org/10.1007/978-1-4614-8265-9_1263
Download citation
DOI: https://doi.org/10.1007/978-1-4614-8265-9_1263
Published:
Publisher Name: Springer, New York, NY
Print ISBN: 978-1-4614-8266-6
Online ISBN: 978-1-4614-8265-9
eBook Packages: Computer ScienceReference Module Computer Science and Engineering