Normalization in DBMS

Normalization in Database Management System is a structured and well defined systematic, step-by-step process of organising the data in the database to minimises the redundancy. It is also used to eliminate unwanted anomalies during Insertion, Update, and Deletion.

This Section is able to tech and Answer various DBMS Interview Questions related to Normalization. After reading this Article you will able to answer the DBMS Interview Questions related to Normalization, Normal Form, Functional Dependency, 1NF,2NF,3NF and BCNF.

What is the role of Normalization in database design?

To reduce redundancy from the database or individual table.

How to achieve Normalization?

By dividing the larger table into the smaller table and linking them using relationship.

What are the normal forms and their types?

For a table to be in certain normal form it has followed certain rules; if it does so then the table is said to be in that particular normal form. Its types are 1st, 2nd, 3rd & Boyce-Codd Normal form.

What are anomalies and their types?

Relations that have redundant data may have problems called anomalies. They can of type: Insertion, Update, and Deletion Anomalies.

Explain different types of anomalies in DBMS?

  • Insertion anomalies: When a tuple/record is tried to be inserted in referencing relation without it being present in the referenced table; it will cause an Insertion Anomaly.
  • Deletion & Update/ Modification anomalies: When a tuple is deleted or updated from referenced relation and the referenced attribute value is used by referencing attribute in referencing relation, it will not allow deleting the tuple from referenced relation. To avoid such a situation: ON UPDATE/DELETE (SET NULL/CASCADE) is used for setting referenced attribute null or update/delete affected record/row/tuple.

To completely understand the concept of Normalization and normal forms, we need to understand what functional dependency is. So, let’s dive in:

What is Functional Dependency in DBMS?

Functional Dependency describes the interrelation of columns within a table; i.e. when values in one field depend on 1 or more other fields within the same table.

For example, there’s a table/ relation to store data of people within a locality who are eligible to get a driving license. The structure of the table is: (name, age, eligibility). It is clearly known that the field eligibility depends on the age of the person, so “eligibility” is functionally dependent on “age”. (age-> eligibility)

How many types of Functional Dependencies are there in DBMS?

FD can be of types:

  1. Trivial FD – where 1 is a subset of other
  2. Non-trivial FD – when related field/s are not subsets of other
  3. Transitive FD – col1 ->col2 -> col3 indicates that if we know col1, col2 could be known, and if we know col2, col3 could be known

What is Normal Form and how many types of Normal Form are there in DBMS?

The state of the Data Table when there is no redundancy and table is the best organized is known as Normal Form.

Following types of Normal Forms are there:

  1. 1st Normal Form or 1 NF
  2. 2nd Normal Form or 2 NF
  3. 3rd Normal Form or 3 NF
  4. Boyce-Codd Normal Form or BCNF

1st Normal Form or 1 NF

A relation is said to be in 1NF if it contains an atomic value for every attribute in a record, i.e. no attribute can be multi-valued.

Conversion Step needed: To enter multi-valued attributes in multi-rows by copying other single valued attributes.

2nd Normal Form or 2 NF

2 NF is a relation that is in 1 NF and every non-primary-key attribute is fully functionally dependent on the primary key. This conversion involves the removal of partial dependencies.

Conversion Step needed: Remove FD attributes from the table and place them in a new table.

3rd Normal Form or 3 NF

A relation is said to be in 3NF if it is in 2 NF and no non-primary-key attribute is transitively dependent on the primary key. This conversion involves removal of transitive dependencies if any.

Conversion Step needed: To remove transitive dependency. Eg: address (Line 1,2,3, Street, City, State, PIN code) need to be made as different table and indexed as a unique value and not included directly into Person/ Student/ Employee table.

Boyce-Codd Normal Form or BCNF

A relation is said to be in BCNF if it is in 3 NF and for each functional dependency (X → Y), X should be a super Key.

Conversion Step needed: Decompose FD table further if needed. Eg: for a dependency A → B, A cannot be a non-prime attribute Health Fitness Articles, if B is a prime attribute.

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