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Find Super and Candidate Key from Attribute Closure

You should know: Before seeing this chapter please follow the previous chapter: Concept of Attribute Closure.

Find Super Key using Attribute Closure

We can find the super key from attribute closure. If we will get total relational (all attributes) by closer of one attribute then this attribute is called the super key.

Example:

So, attribute A is the super key of this relation (A → Super Key)

Find candidate key from attribute closure:

Example:

Let a relation R (ABCD) and functional dependencies are {AB → C, C → D, B → E}

So, we can say AB is Super Key of this relation or table.

Now,

If the super key is minimal then it is also candidate key like above example A is super key and candidate key also.

Now we check AB which is S.K, is minimal or not. 

So, AB is minimal. So, it is the candidate key also.

The reason is key attributes uniquely identify all tuples.

So, the closer of any key attribute always derive whole relation or table, so, any key attribute functionally determined any non-key attribute.

Those are the main concept.