Example: Constraints on Entity Set
Consider relation obtained from Hourly_Emps:
- Hourly_Emps (ssn, name, lot, rating, hrly_wages, hrs_worked)
Notation: We will denote this relation schema by listing the attributes: SNLRWH
- This is really the set of attributes {S,N,L,R,W,H}.
- Sometimes, we will refer to all attributes of a relation by using the relation name. (e.g., Hourly_Emps for SNLRWH)
Some FDs on Hourly_Emps:
- ssn is the key: S SNLRWH
- rating determines hrly_wages: R W