Functional Dependencies(Cont.) K is a superkey for relation schema R if and only if K->R K is a candidate key for R if and only if K→R,and for no ac K,→R Functional dependencies allow us to express constraints that cannot be expressed using superkeys.Consider the schema: bor loan =(customer id,loan number,amount ) We expect this functional dependency to hold: loan number-→amount but would not expect the following to hold: amount->customer name Database System Concepts-5th Edition,Oct 5,2006 7.13 ©Silberschat乜，Korth and SudarshanDatabase System Concepts - 5 7.13 ©Silberschatz, Korth and Sudarshan th Edition, Oct 5, 2006 Functional Dependencies (Cont.) K is a superkey for relation schema R if and only if K → R K is a candidate key for R if and only if K → R, and for no   K,  → R Functional dependencies allow us to express constraints that cannot be expressed using superkeys. Consider the schema: bor_loan = (customer_id, loan_number, amount ). We expect this functional dependency to hold: loan_number → amount but would not expect the following to hold: amount → customer_name