Functional dependency: Difference between revisions

Revision as of 11:35, 21 March 2023

Revision as of 05:13, 6 July 2023

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Imagine the following list of FDs. We are going to calculate a closure for A from this relationship.

1.# ''A'' → ''B'' <br/>

2.# ''B'' → ''C'' <br/>

3.# ''AB'' → ''D''

The closure would be as follows:

{{ordered list | list-style-type = lower-alpha

a)| A → A (by Armstrong's reflexivity) <br/>

b)| A → AB (by 1. and (a)) <br/>

c)| A → ABD (by (b), 3, and Armstrong's transitivity) <br/>

d)| A → ABCD (by (c), and 2)

}}

The closure is therefore A → ABCD. By calculating the closure of A, we have validated that A is also a good candidate key as its closure is every single data value in the relationship.