Advanced Database Management System - Tutorials and Notes: Find the closure of set of attributes

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Sunday, 8 May 2016

Find the closure of set of attributes

Find the closure of set of attributes, Check whether the given attributes forms candidate keys, How to find closure of attributes? Find closure - solved exercise, Check for unique determination of an attribute by the other attribute


Question:
2. Let F = {A B, A C, BC D}. Can A determine D uniquely?

Solution:
To find this, we need to find the closure of A.
Closure:
In simple terms, if you know an attribute (or set of attributes) in a relation R, then what other attribute (or set of attributes) you would determine uniquely is called the closure. We normally find the closure of left hand side (LHS) attributes of the functional dependencies of relation R. Closure is used to find the candidate keys of the relation. Refer here to know more about attribute closure.

To find A+:
result := A
result := AB from the functional dependency (FD) A B
result := ABC from the FD A C
result := ABCD from the FD BC D

The closure of attribute A is ABCD. And the closure includes the attribute D in it. Hence, values of attribute A can uniquely determine the values of attribute D.

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