DBMS Notes

Relational Decomposition

  • When a table in the relational model is not in appropriate normal form then the decomposition of a relation is required.
  • In a database, it breaks the table into multiple tables.
  • If the table does not decompose properly, then it may lead to some problems like loss of information or insertion of some new information’s.

Need of Relational decomposition

When we decompose the table then

  • Decomposition should be either lossless or dependency preserving.
  • Such decomposition will always be safe and no information’s will be lost otherwise record may be changed or lost.

So Decomposition should be

  1. Lossless Decomposition
  2. Dependency Preserving

1. Lossless Decomposition

  • If the information’s are not lost from the relation after its decomposing, then the decomposition will be lossless.

2. Dependency Preserving

The decomposition of relation (R) with FD’s (F), into R1 and R2 with their FD’s (F1) and (F2) respectively is said to be dependency preserving if.

Closure of F (F+) = Closure of F1 (F1+) U Closure of F2 (F2+)

In next lecture we will explain these types in detail

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