Keys Let KcR K is a superkey of R if values for K are sufficient to identify a unique tuple of each possible relation r(R) Example:{ID}and {ID,name}are both superkeys of instructor. Superkey K is a candidate key if K is minimal Example:{ID}is a candidate key for Instructor One of the candidate keys is selected to be the primary key. which one? Foreign key constraint:Value in one relation must appear in another Referencing relation Referenced relation Example-dept name in instructor is a foreign key from instructor referencing department Database System Concepts-6th Edition 2.6 @Silberschatz,Korth and SudarshanDatabase System Concepts - 6 2.6 ©Silberschatz, Korth and Sudarshan th Edition Keys Let K  R K is a superkey of R if values for K are sufficient to identify a unique tuple of each possible relation r(R) Example: {ID} and {ID,name} are both superkeys of instructor. Superkey K is a candidate key if K is minimal Example: {ID} is a candidate key for Instructor One of the candidate keys is selected to be the primary key. which one? Foreign key constraint: Value in one relation must appear in another Referencing relation Referenced relation Example – dept_name in instructor is a foreign key from instructor referencing department