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.
翻译：传统上,人们同意,关系数据库可以逐步正常化,从一组未经调整的表格到以1美元计算的表格,再到2美元,再到3美元,然后(可能)再到3美元,再到1美元,然后(可能)再到1美元。该规则适用于1美元,以便将其转换成以2美元计算的表格,这似乎过于简单,无法造成任何困难。然而,我们表明,根据一系列功能依赖性,不可能达到2美元,再到那里止;在这种情况下,必须实现从1美元到3美元这一正常化,作为不可弥补的举动。 展示这一现象的最低限度设置需要单一的复合钥匙和两个部分重叠的过境依赖性链。
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