3.1.07. Functional dependency

  • 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