#KPC #CST #Relational Decomposition
- 1. Relational Decomposition Arvin Bera (Lecturer CST KPC)
- 2. Learning Outcome Types of Decomposition Lossless Decomposition Dependency Preserving
- 4. Lossless Decomposition If the information is not lost from the relation that is decomposed, then the decomposition will be lossless. The lossless decomposition guarantees that the join of relations will result in the same relation as it was decomposed. The relation is said to be lossless decomposition if natural joins of all the decomposition give the original relation.
- 5. Example
- 6. Example
- 7. Example
- 8. Lossy Decomposition As the name suggests, when a relation is decomposed into two or more relational schemas, the loss of information is unavoidable when the original relation is retrieved.
- 10. Dependency Preserving It is an important constraint of the database. In the dependency preservation, at least one decomposed table must satisfy every dependency. If a relation R is decomposed into relation R1 and R2, then the dependencies of R either must be a part of R1 or R2 or must be derivable from the combination of functional dependencies of R1 and R2.
- 11. Dependency Preserving For example, suppose there is a relation R (A, B, C, D) with functional dependency set (A->BC). The relational R is decomposed into R1(ABC) and R2(AD) which is dependency preserving because FD A->BC is a part of relation R1(ABC).
- 12. Example R(A,B,C,D,E) {AB->C,B->D,D->E} (AB)+=>ABCDE B=>D B is the partial key So the relation is not in 2NF So we have to decompose this relation into two parts ABC and BDE Now we have to decompose the BDE into two parts BD and DE Here all the FD’s are reserved decomposition