Key dependencies is generalization of functional dependencies - Database

Q.  What is the generalization of functional dependencies?
- Published on 27 Aug 15

a. Database dependencies
b. Key dependencies
c. Relation dependencies
d. None of these

ANSWER: Key dependencies

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    Discussion

  • Nirja Shah   -Posted on 30 Oct 15
    Functional dependencies
    - Constraints on the set of legal relations.

    - Require that the value for a certain set of attributes determines uniquely the value for another set of attributes.

    - A functional dependency is a generalization of the notion of a key.

    Use functional dependencies

    - They test the 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 .

    - The constraints are specified 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 .

    - 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-schema may, by chance, satisfy loan-number
    - customer-name.

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