What is Lossless join property?
2555
22-Sep-2014
Aryan Kumar
28-Apr-2023In database management systems, the lossless join property is a property of a decomposition of a relation into multiple smaller relations. A decomposition is said to have the lossless join property if and only if it is possible to join the smaller relations back together to form the original relation without losing any information.
In other words, if we decompose a relation into multiple smaller relations, and then join these smaller relations back together, we should get the same result as if we had not decomposed the relation at all.
A lossless join decomposition ensures that no information is lost during the decomposition process, which is important in database design to avoid data inconsistencies or loss.
For example, consider a relation R(A, B, C, D) with the functional dependencies A -> B and BC -> D. We can decompose this relation into two smaller relations: R1(A, B) and R2(B, C, D). This decomposition has the lossless join property because we can join R1 and R2 back together on the common attribute B to get the original relation R.
If a decomposition does not have the lossless join property, it means that information is lost during the decomposition process, which can lead to data inconsistencies or loss. Therefore, it is important to ensure that any decomposition of a relation into smaller relations has the lossless join property.
Sumit Kesarwani
22-Sep-2014It guarantees that the spurious tuple generation does not occur with respect to relation schemas after decomposition.