Join dependency in DBMS is a generalization upon the concept of multivalued dependency.
- Let the joining of the two relations R1 and R2 with C be equal to the relation that is R. Then it is safe to conclude that there is a join dependency.
- R1 and R2 constitute the decomposition of R2 (C, D) and R1(A, B, C) of the relation R(A, B, C, D).
- As an alternative, R2 and R1 constitute the lossless breakdown of R.
- A join dependency (R1, R2, R3., R4,….., Rn) holds over R if R1, R2, R3, R4,…Rn constitute a lossless type of join decomposition.
- *(A, B, C, D), (C, D) represent a join dependency of R if join’s attribute’s joining is equal to R.
- In this equation, *(R1, R2, R3) indicates that R1, R2, R3,…., Rn constitute a join dependency on R.