Dependency Preserving Decomposition in DBMS

Dependency Preserving Decomposition in DBMS

 

In this article, we will learn about the Dependency Preserving Decomposition in DBMS.

  • Decomposition of a relation in relational model is done to convert it into appropriate normal form
  • A relation R is decomposed into two or more only if the decomposition is both lossless join and dependency preserving.

 

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Dependency Preserving Decomposition in DBMS

Dependency Preserving Decomposition

  • If we decompose a relation R into relations R1 and R2, all dependencies of R must be part of either R1 or R2 or must be derivable from combination of functional dependencies(FD) of R1 and R2
  • Suppose a relation R(A,B,C,D) with FD set {A->BC} is decomposed into R1(ABC) and R2(AD) which is dependency preserving because FD A->BC is a part of R1(ABC).

 

Example

Consider a schema R(A,B,C,D) and functional dependencies A->B and C->D which is decomposed into R1(AB) and R2(CD)

This decomposition is dependency preserving decompostion because

  • A->B can be ensured in R1(AB)
  • C->D can be ensured in R2(CD)