3.1.09. Functional dependency

  • If X is a key (primary and/or candidate)
    • All tuples ti have a unique value for X
    • No two tuples (t1,t2) share a value of X
  • Therefore X -> Y
    • For any subset of attributes Y
  • Examples
    • SSN -> {Fname, Minit, Lname}
    • {Country of issue, Driving license no} -> SSN
    • Mobile area code -> Mobile
      network (not anymore)