Database/DBMS Interview Questions And Answers

Database/DBMS Interview Questions And Answers - Part XI.

51) What Is Normalization. Explain It In Detail?

Answer: Normalization is the process of organizing and designing a data model to efficiently store data in a database. The end result is that redundant data is eliminated, and only data related to the attribute is stored within the table. In short, Normalization is a process of decomposing unsatisfactory "bad" relations by breaking up their attributes into smaller relations.

Normal forms reduce the amount of redundancy and inconsistent dependency within databases. Normalization organizes the data into tables where each item is a row and the attributes of the item are in columns.

Redundant data wastes disk space and creates maintenance problems. If data that exists in more than one place must be changed, the data must be changed in exactly the same way in all locations. For example: An employee address change is much easier to implement if that data is stored only in the Employee table and nowhere else in the database.

Normalizing the database ensures the following things:

Dependencies between data are identified.
Redundant data is minimized.
The data model is flexible and easier to maintain.

52) What Is The Need For Normalization In DBMS?

Answer: Database normalization, or data normalization, is a technique to organize the contents of the tables for transactional databases and data warehouses.

There is a need for normalization in DBMS because:

To eliminate data redundancy.
To eliminate data inconsistency.
To not have null values in key attributes.

Normalization prevents the possible corruption of databases stemming from what are called 'Insertion anomalies', Deletion anomalies' and 'Update anomalies'.

Normalization is part of successful database design; without normalization, database systems can be inaccurate, slow, and inefficient, and they might not produce the data you expect.

53) What Are The Goals Of Normalization In DBMS?

Answer: Goals of normalization are:

Eliminate redundancies caused by:

 Fields repeated within a table.
 Fields not directly describing the key entity.
 Fields derived from other fields.

Avoid anomalies in updating (Adding, Editing and Deleting)
Represent accurately the items being modeled.
Simplify maintenance & retrieval of info.

54) State The Benefits Of Normalization In DBMS?

Answer: The benefits of normalization are:

Facilitates data integration.
Reduces data redundancy.
Provides a robust architecture for retrieving and maintaining data.
Compliments data modeling.
Reduces the chances of data anomalies.
Decreased storage requirements.
Faster search performance because of smaller files for table scan and more directed searching.

55) What Is Functional Dependency?

Answer: A functional dependency is an association between two attributes of the same relational database table. Functional dependencies (FDs) are used to specify formal measures of the "goodness" of relational designs.

FDs and keys are used to define normal forms for relations. FDs are constraints that are derived from the meaning and interrelationships of the data attributes

X->Y: A set of attributes X functionally determines a set of attributes Y if the value of X determines a unique value for Y.
X -> Y holds if whenever two tuples have the same value for X, they must have the same value for Y.

For example, if X and Y are attributes of relation R, Y is said to be functionally dependent on X (denoted X → Y), if each value of X in R is associated with exactly one value of Y in R.

For example, in an "Employee" table that includes the attributes "Employee ID" and "Employee Date of Birth", the functional dependency {Employee ID} → {Employee Date of Birth} would hold.

ALSO CHECK THE BELOW FAQ's:

56) What Is Fully Functional Dependency?
57) What Is Partial Dependency?
58) What Is Transitive Dependency?
59) What Is A Trivial Functional Dependency?
60) What Is Multivalued Dependency?

61) What Are The Steps Of Normalization?
62) What Is First (1st) Normal Form (1NF)?
63) What Is Second (2nd) Normal Form (2NF)?
64) What Is Third (3rd) Normal Form (3NF)?
65) What Is Boyce-Codd Normal Form (BCNF)? Also Define Multivalued Dependency?

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