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Thursday, 28 August 2014
Various uses of attribute closure
1. Used to check whether an attribute (or set of attributes) forms a key or not.
Use the algorithm discussed in the posts “How to find closure of attributes in DBMS?” Or “How to find key of a given table? - Analternate way”.
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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