## 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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