Limitations of Join Dependency
- Complexity: The database becomes more and more complex as we have to create multiple sub-tables/sub-relations which leads to an increase in the number of tables/relations
- Cost: For large databases, the decomposition can be quite costly
- Reduced Performance: Due to the large number of tables, query performance will be reduced as it will take time to traverse through multiple tables/relations present in the database.
Join Dependency in Database
Join Dependency means re-creating the original Table by joining multiple sub-tables of the given Table. It is a further generalization of MVD(multi-valued Dependencies).
- When a relation R can be obtained by joining the R1, R2, R3…, Rn where R1, R2, R3…, Rn are sub-relations of R, it is called a Join Dependency.
- R1,R2,R3…Rn are the sub-relations composed or derived from the relation R.