Thursday, 28 August 2014

Various uses of attribute closure


What are the uses of attribute closure A+ / Purposes of finding attribute closure / Attribute closure in DBMS


Several uses of attribute closure:

1. Used to check whether an attribute (or set of attributes) forms a key or not.
2. Used to find easily all the functional dependencies hold in a relation.
For example, to check whether a FD like A B holds in a relation, find the A+. If B is in A+, then the functional dependency A B is valid.
3. Used as an alternate way to find Closure of FDs (F+).
For every attribute or set of attributes on the left hand side of the arrow in a functional dependency, find the Closure. This process results in F+.





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