Use of Functional Dependencies We use functional dependencies to: test relations to see if they are legal under a given set of functional dependencies. If a relation r is legal under a set F of functional dependencies,we say that rsatisfies F. specify constraints on the set of legal relations We say that F holds on R if all legal relations on R satisfy the set of functional dependencies F. Note:A specific instance of a relation schema may satisfy a functional dependency even if the functional dependency does not hold on all legal instances. For example,a specific instance of loan may,by chance,satisfy amount->customer name. Database System Concepts-5th Edition,Oct 5,2006 7.14 ©Silberschat乜，Korth and SudarshanDatabase System Concepts - 5 7.14 ©Silberschatz, Korth and Sudarshan th Edition, Oct 5, 2006 Use of Functional Dependencies We use functional dependencies to: test relations to see if they are legal under a given set of functional dependencies.  If a relation r is legal under a set F of functional dependencies, we say that r satisfies F. specify constraints on the set of legal relations  We say that F holds on R if all legal relations on R satisfy the set of functional dependencies F. Note: A specific instance of a relation schema may satisfy a functional dependency even if the functional dependency does not hold on all legal instances. For example, a specific instance of loan may, by chance, satisfy amount → customer_name