Relational databases depends on tables, columns, rows or schemas to arrange systematically thedata and retrieve it. A NoSQL originally refers to non-Structured Query Language or nonrelational database giving a structure for storing and getting data that is presented in means otherthan the tabular form or relations likewise used in “relational databases”. Such databases existedfrom late 90’s, but didn’t obtain the NoSQL brand until a rise of popularity in the earlytwenty-first century, caused by the needs of Web 2.0 companies such as Yahoo, Facebook,Google, and Amazon. NoSQL databases are increasingly used in big data and real-time webapplications. These are also called Not only SQL for the fact that they may support SQL-likequery languages.Why the need of NoSQL?RDBMSs operate with a relational model defined by schema, where each table is a strictlydefined collection of rows and columns and a relationship can then be established between eachrow in one table and a row in another table. Relational data can be queried and manipulated byusing SQL query language. To prevent the inconvenience to store data in the form of tables orwe have other kind of relationships between records and want to quickly access the data.Why nosql preferred over sql :-In many of the cases, how the use of RDBMSs leads to problems due to fixed schema, whichmakes them ill-suited for changing business requirements, as schema changes are problematicand time-consuming, causing insufficient performance and latency for the new requirements andlimited ability to scale cost-effectively. The data structures used e.g. key-value, wide column,graph, or document are different from default used in RDBMSs, making some operations fasterand more flexible sometimes.The main reason not to use an SQL database is scalability, especially given the write-heavyworkloads generated by modern web applications. For example: An app like Facebook can’t bemade to work on a straightforward SQL database, except by massive partitioning and slicing,which requires important adjustment to the application logic also, so Facebook developedCassandra.Ankesh Kumar Suman2K15/MC/11Types of nosql databases model and their classification with examples:? Wide-Column : This type of databases just like RDBMSs stores data in tables, butnames and formats of columns can differ from row to row across the table. It groupsrelated columns data collective. E.g. Accumulo, Cassandra, Druid, HBase, Vertica.? Document :This typically stores described BSON, JSON and XML documents. E.g.Apache CouchDB, ArangoDB, BaseX, Clusterpoint, Couchbase, Cosmos DB, IBMDomino, MarkLogic, MongoDB, OrientDB, Qizx, RethinkDB? Key-value : This type provides importance to simplicity and useful in speedilyallowing an application to support faster read and write processing ofnon-transactional data. e.g. Aerospike, Apache Ignite, ArangoDB, Couchbase,Dynamo, FairCom c-treeACE, FoundationDB, InfinityDB, MemcacheDB, MUMPS,Oracle NoSQL Database, OrientDB, Redis, Riak, Berkeley DB, SDBM/Flat File dbm? Graph : This type of databases uses graph structures to query, store and map,relationships. It allows adjacent elements to linked together without using an index.E.g. AllegroGraph, ArangoDB, InfiniteGraph, Apache Giraph, MarkLogic, Neo4J,OrientDB, Virtuoso? Multi-model : They accumulate some combination of the above described andsupport a broad number of applications. E.g. Apache Ignite, FoundationDB,ArangoDB, Couchbase, MarkLogic, InfinityDB, OrientDBKey benefits:NoSQL are column oriented databases instead of being row oriented. It seems to work better on both non-related andnon-structured data.NoSQL databases give up some features of the traditional databases for speed and horizontalscalability.NoSQL databases are seems to be safer, faster and cheaper to continue an existing programinstead of doing it from scratch.Nowaday’s applications are required to run continuously and effectually manage the growing amounts of multi-structured data. This is the reason which leads to the need of NoSQLfrom something to a serious consideration for every database from small to the big enterprise.