UNIT II DATABASE DESIGN

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2.6 Lossless Decomposition

A lossless decomposition is a process of decomposing a relation schema into multiple relations in such a way that it preserves the information contained in the original relation.

  • Joining the decomposed tables gives back the original table.
  • No extra or missing rows are created.
lossless_decomposition_example_
Example of Lossless Decomposition

Conditions for Lossless Decomposition

  • After decomposition, the union of attributes of X₁ and X₂ must be equal to the attributes of the original relation X.
  • X₁ and X₂ must have at least one common attribute (intersection should not be NULL).
  • The common attribute must be a super key in at least one of the decomposed relations (X₁ or X₂).
  • The common attribute should have unique values to ensure a lossless join.

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