Question :

What do you mean by lossless join? How can we test it.

Subject

Database Management System

Standard

Computer Science Engineering

Views

562

Asked By

Thomas

Krishav
Answer / Solution

Lossless-join decomposition is a process in which a relation is decomposed into two or more relations. This property guarantees that the extra or less tuple generation problem does not occur and no information is lost from the original relation during the decomposition.

For lossless join decomposition, we select a common attribute. Attributes in DBMS are the descriptive properties which describe an entity

In addition, the following conditions must also be satisfied-

  • The union of the sub-relations Relation-1 and Relation-2 should be containing all the attributes that were present in the original relation R which got decomposed.
  • The intersection of sub-relations Relation-1 and Relation-2 is not allowed to be null. It is necessary for the sub-relation to contain a common attribute.

It is also known as non-additive join decomposition. The two main conditions for lossless join decomposition are

  1. The union of the sub-relations R1 and R2 must contain all the attributes that are available in the original relation R before decomposition
  2. The intersection of sub-relations R1 and R2 cannot be null.

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