- Constraint between two sets of attributes
- Formal method for grouping attributes
- DB as one single universal relation/-literal
- R = {A1,A2,…,An}
- Two sets of attributes, X subset R,Y subset R
- Functional dependency (FD or f.d.) X -> Y
- If t1[X] = t2[X], then t1[Y] = t2[Y]
- Values of the Y attribute depend on value of X
- X functionally determines Y, not reverse necessarily
In Focus
3.1.07. Functional dependency