Temporal Query Languages(Cont.) Functional dependencies must be used with care:adding a time field may invalidate functional dependency A temporal functional dependency x>Y holds on a relation schema R if,for all legal instances r of R,all snapshots of r satisfy the functional dependency X->Y. SQL:1999 Part 7(SQL/Temporal)is a proposed extension to SQL:1999 to improve support of temporal data. Database System Concepts-6th Edition 25.7 @Silberschatz,Korth and SudarshanDatabase System Concepts - 6 25.7 ©Silberschatz, Korth and Sudarshan th Edition Temporal Query Languages (Cont.) Functional dependencies must be used with care: adding a time field may invalidate functional dependency A temporal functional dependency x → Y holds on a relation schema R if, for all legal instances r of R, all snapshots of r satisfy the functional dependency X →Y. SQL:1999 Part 7 (SQL/Temporal) is a proposed extension to SQL:1999 to improve support of temporal data. 