Intro to DBMS

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.

Need for 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 will be lost; otherwise, the record may be changed or lost.

So, Decomposition should be

  1. Lossless Decomposition
  2. Dependency Preserving

1. Lossless Decomposition

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

2. Dependency Preserving

The decomposition of relation (R) with FDs (F) into R1 and R2 with their FDs (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 the next lecture, we will explain these types in detail