The main task in relational schema normalization is producing such a set of schemas that posses the required form, usually 3NF or BCNF.
A schema is in BCNF if only the first condition of the two above is allowed.
On contrast, BCNF eliminates all redundancies but does not preserve all dependencies.
2] is not in BCNF, since delivPlace is not a superkey in [R.
A lossless join decomposition of R, which is in BCNF, is said to be optimum if it has the smallest possible size.
is monodependent), if and only if every lossless join decomposition of R is also dependency preserving, and show that a unique, optimum, lossless join decomposition of R, which is in BCNF and is also dependency preserving, can be obtained in polynomial time in the size of F.
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
We first formalize the concepts of 2NF, 3NF, and BCNF [Ullman 1988; Mannila and Raiha 1992; Atzeni and De Antonellis 1993].
To remove data redundancy, if we use the FDs corresponding to constraints 1 and 2, we obtain the following BCNF decomposition for COURSES: (Course#, Credits) and (Course#, Lab-Assist, Lab-Assist-Pay, #Students-in-Class, Day).
The central part of the article gives the definitions of temporal BCNF (TBCNF) and temporal 3NF (T3NF) and algorithms for achieving TBCNF and T3NF decompositions.
Regarding decomposition algorithms, it is natural to think of the following naive approach:(3) add additional attributes, such as week and month, to the original scheme and then apply standard decomposition techniques, such as BCNF decomposition.
Likewise, a temporal relation is in temporal Boyce-Codd normal form if each snapshot is in BCNF.