Tutorial By Namitha

Dependency Preserving Decomposition  If we decompose a relation R into relations R1 and R2, All dependencies of R either must be a part of R1 or R2 or must be derivable from   FD’s of R1 and R2 .    Relation R is decomposed in to R1 and R2 with FDs F1 and F2 respectively  ,  if the decomposition is dependency preserving then F1 U F2 =F                                                and so           ( F1 U F2 ) + =F+

Normalization is the process of minimizing redundancy and eliminating anomalies from a relation or a set of relations.  Decomposition of a relation is done when a relation is not in required normal form .   We can decompose a relation into two or more relations if decomposition is lossless join as well as dependency preserving.  Upto 3rd normal form both of these decomposition properties we need to preserve.  Given a relation R after decomposing R into R1 and R2  , If R1 join R2 =R ,then the decomposition is said to be lossless join decomposition . If R1 join R2 is ⊃ R ,then the decomposition is said to be lossy decomposition .