It is the process of eliminating redundant data and maintaining data dependencies.

NoSQL is better than RDBMS because of the following reasons/properities of NoSQL:

• It supports semi-structured data and volatile data
• It does not have schema
• Read/Write throughput is very high
• Horizontal scalability can be achieved easily
• Will support Bigdata in volumes of Terra Bytes & Peta Bytes
• Provides good support for Analytic tools on top of Bigdata
• Can be hosted in cheaper hardware machines
• In-memory caching option is available to increase the performance of queries
• Faster development life cycles for developers

Still, RDBMS is better than NoSQL for the following reasons/properties of RDBMS:

• Transactions with ACID properties - Atomicity, Consistency, Isolation & Durability
• Adherence to Strong Schema of data being written/read
• Real time query management ( in case of data size < 10 Tera bytes )
• Execution of complex queries involving join & group by clauses

• Atomicity: It ensures all-or-none rule for database modifications.
• Consistency: Data values are consistent across the database.
• Isolation: Two transactions are said to be independent of one another.
• Durability: Data is not lost even at the time of server failure.

It is the process of improving the performance of the database by adding redundant data.

• A clustered index is a special type of index that reorders the way records in the table are physically stored. Therefore table can have only one clustered index. The leaf nodes of a clustered index contain the data pages.
• A non clustered index is a special type of index in which the logical order of the index does not match the physical stored order of the rows on disk. The leaf node of a non clustered index does not consist of the data pages. Instead, the leaf nodes contain index rows.