From Wikipedia, the free encyclopedia

In computer science the concept of a Lossless-Join Decomposition is central in removing redundancy safely from databases while preserving the original data.

Contents [hide] 1 Lossless-join Decomposition 2 Example 3 Normal Forms 4 References

[edit]Lossless-join Decomposition

Can also be called Nonadditive. If you decompose a relation  into relations  and  you will guarantee a Lossless-Join if ⋈ = .

Let  be a relation schema.

Let  be a set of functional dependencies on .

Let  and  form a decomposition of .

The decomposition is a lossless-join decomposition of R if at least one of the following functional dependencies are in ⁺(where ⁺ stands for the closure for every attribute in ):^[1]

•  ∩  → 


•  ∩  → 

[edit]Example

• Let  be the relation schema, with , ,  and  attributes.


• Let  be the set of functional dependencies.


• Decomposition into  and  is lossless under  because  and  so .

[edit]Normal Forms

Decomposition into BCNF or 3NF must always be lossless.

[edit]References