Is 2NF a Stable Normal Form?

06/29/2021

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by   Amir Sapir, et al.

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Traditionally, it was accepted that a relational database can be normalized step-by-step, from a set of un-normalized tables to tables in 1NF, then to 2NF, then to 3NF, then (possibly) to BCNF. The rule applied to a table in 1NF in order to transform it to a set of tables in 2NF seems to be too straightforward to pose any difficulty. However, we show that, depending on the set of functional dependencies, it is impossible to reach 2NF and stop there; one must, in these cases, perform the normalization from 1NF to 3NF as an indecomposable move. The minimal setup to exhibit the phenomena requires a single composite key, and two partially overlapping chains of transitive dependencies.