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Can also be called Nonadditive. 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.
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):
- 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 .
- Pohler, K (2015). "Lossless-Join Decomposition: applications in quantitative computing metrics". International Journal of Applied Computer Science. 21 (4): 190–212.
- "Lossless Join Property". Stackoverflow.com. Retrieved 2016-02-07.
- "Lossless Join Decomposition" (PDF). University at Buffalo. Jan Chomicki. Retrieved 2012-02-08.
- "Lossless-Join Decomposition". Cs.sfu.ca. Retrieved 2016-02-07.
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