Closure of attributes in DBMS Theory - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the closure of a set of attributes in a database?

The closure of a set of attributes is the complete set of attributes that can be functionally determined from the original set using the given functional dependencies.

beginner

Why is finding the closure of attributes important in database design?

It helps to find all attributes that depend on a given set, which is useful for checking keys and normalizing tables.

beginner

What is the first step in computing the closure of a set of attributes?

Start with the original set of attributes and add attributes that can be functionally determined using the functional dependencies until no more can be added.

intermediate

If the closure of an attribute set includes all attributes of a relation, what does that imply?

It means the attribute set is a candidate key for that relation.

intermediate

Can the closure of attributes change if functional dependencies change?

Yes, the closure depends on the functional dependencies. Changing them can add or remove attributes from the closure.

What does the closure of a set of attributes represent?

A Attributes unrelated to the set

B Only the original attributes in the set

C All attributes in the database

D All attributes functionally dependent on the set

The closure includes all attributes that can be functionally determined from the original set.

If the closure of attribute set X includes all attributes of relation R, what is X?

A A candidate key

B A foreign key

C A non-key attribute

D An irrelevant attribute

If X's closure covers all attributes, X is a candidate key.

Which of these is needed to compute the closure of attributes?

A Functional dependencies

B Primary key only

C Foreign keys only

D Data values

Functional dependencies define how attributes determine others, essential for closure.

What happens if you add more functional dependencies to the set when computing closure?

A Closure becomes empty

B Closure always shrinks

C Closure can only stay the same or grow

D Closure is unrelated to dependencies

More dependencies can add more attributes to the closure or keep it the same.

Why is closure useful in normalization?

A To store data faster

B To find keys and remove redundancy

C To encrypt data

D To create indexes

Closure helps identify keys and dependencies, which are important for normalization.

Explain the process of finding the closure of a set of attributes with an example.

Think about how you can find all attributes related to your starting set.

Describe why the closure of attributes is important for identifying candidate keys in a relation.

Consider what it means if your attribute set can determine everything.