Note that partial dependencies, even if violate the 3NF, are not considered in [F.sub.t], because the input relations are supposed already in 2NF using the previous algorithm.
Algorithm 6: Decomposes into 3NF. Input: [R.sub.1], ...,[R.sub.n] relations in 2NF, and the set [F.sub.t].
The main task in relational schema normalization is producing such a set of schemas that posses the required form, usually 3NF
Summary of main complexity results Problem/Class FD IP SF MONO Optimum cover NPC P P P Superkey of NPC NPC P P cardinality k Prime attribute NPC P P P 3NF
NPC P P P Optimum BCNF NPH -- -- P 2.
(2007) state "Relationships in third normal form (3NF
) are sufficient for most practical database applications" (p.
Top-down approaches begin from a set of relations that are in a given normal form (e.g., 1NF or 2NF) and use appropriate methods of decomposition to generate better relations (e.g., 3NF
or BCNF relations).
These dependencies are then used for normalizing the relational schema to 3NF
. A system to derive functional dependencies from forms has also been proposed .
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Both normal forms are proper extensions of their traditional counterparts, BCNF and 3NF
. Decomposition algorithms are presented that give lossless TBCNF decompositions and lossless, dependency-preserving, T3NF decompositions.
The input RDB schema must be in third-normal form (3NF
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In this later paper Codd introduces "second normal form" (2NF) and "third normal form" (3NF