- 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)
In Focus
3.1.09. Functional dependency