Candidate key finding using closure in DBMS Theory - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a candidate key in a database?

A candidate key is a minimal set of attributes that can uniquely identify a tuple (row) in a relation (table). It means no attribute can be removed without losing the uniqueness property.

beginner

What does the closure of a set of attributes represent?

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

intermediate

How is closure used to find candidate keys?

To find candidate keys, we compute the closure of attribute sets. If the closure contains all attributes of the relation, that set is a superkey. Minimal superkeys are candidate keys.

beginner

What is the difference between a superkey and a candidate key?

A superkey is any set of attributes that uniquely identifies tuples. A candidate key is a minimal superkey, meaning it has no unnecessary attributes.

beginner

Why do we look for minimal attribute sets when finding candidate keys?

Minimal attribute sets avoid redundancy and ensure the key is as simple as possible while still uniquely identifying tuples.

What does the closure of an attribute set tell us?

A The total number of attributes in the relation

B All attributes functionally determined by that set

C The primary key of the table

D The number of tuples in the table

Closure shows all attributes that can be derived from the given attribute set using functional dependencies.

If the closure of an attribute set includes all attributes of the relation, what is it called?

A Superkey

B Foreign key

C Candidate key

D Partial key

A superkey is any attribute set whose closure contains all attributes of the relation.

What makes a candidate key different from a superkey?

A Candidate key has foreign keys

B Candidate key is larger

C Candidate key is not unique

D Candidate key is minimal

Candidate keys are minimal superkeys with no extra attributes.

Which of these is NOT true about candidate keys?

A They can have redundant attributes

B They uniquely identify tuples

C They are minimal

D There can be multiple candidate keys

Candidate keys must be minimal and cannot have redundant attributes.

Why do we use closure to find candidate keys?

A To find the largest attribute set

B To count the number of tuples

C To find all attributes functionally dependent on a set

D To delete redundant data

Closure helps identify if an attribute set can determine all attributes, indicating a superkey or candidate key.

Explain how to use closure to find candidate keys in a relation.

Think about how closure helps find superkeys and then minimal superkeys.

What is the difference between a superkey and a candidate key? Why is minimality important?

Focus on uniqueness and minimal attribute sets.