Lossless-Join Decomposition

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In computer science the concept of a Lossless-Join Decomposition is central in removing redundancy safely from databases while preserving the original data.[1]

Lossless-join Decomposition[edit]

Can also be called Nonadditive.[citation needed] If you decompose a relation R into relations you will guarantee a Lossless-Join if .

If R is split into and , for the decomposition to be lossless then at least one of the two should hold true.

Projecting on and , and joining back, results in the relation you started with.[2]

Let R be a relation schema.

Let F be a set of functional dependencies on R.

Let and form a decomposition of R.

The decomposition is a lossless-join decomposition of R if at least one of the following functional dependencies are in F+ (where F+ stands for the closure for every attribute or attribute sets in F):[3]


  • Let be the relation schema, with A, B, C and D attributes.
  • Let be the set of functional dependencies.
  • Decomposition into and is lossless under F because , A is a superkey in ( ) so .



  1. ^ Pohler, K (2015). "Lossless-Join Decomposition: applications in quantitative computing metrics". International Journal of Applied Computer Science. 21 (4): 190–212.
  2. ^ "Lossless Join Property". Stackoverflow.com. Retrieved 2016-02-07.
  3. ^ "Lossless Join Decomposition" (PDF). University at Buffalo. Jan Chomicki. Retrieved 2012-02-08.
  4. ^ "Lossless-Join Decomposition". Cs.sfu.ca. Retrieved 2016-02-07.
  5. ^ [1][dead link]