NoSQL databases are designed for large data storage needs in distributed databases. Unlike SQL databases, NoSQL databases do not use SQL for queries and are schema-free, horizontally scalable, and fault tolerant. The main categories of NoSQL databases are document oriented, XML based, graph databases, and key-value stores. Major tech companies like Google, Facebook, and Amazon use NoSQL databases like BigTable, Cassandra, and DynamoDB.

1. NoSQL Databases
By:
Ashish Karki

2. Definition
 Acronym stands for Not Only SQL.
 Designed for Distributed Databases
with large data storing needs.
 Does not use SQL as its query
language.
 Coined by Carlo Strozzi in the year
1998

3. Important Characteristics
 Schema-free
 Horizontally-scalable
 Distributed and fault-tolerant
architecture
 Non-compliance with ACID properties.

4. Categories
Categories Description Examples
Document Oriented Data is stored as a set MongoDB, CouchDB
of documents
containing objects.
Follows JSON format to
store objects.
XML Based Data is stored in XML BaseX
format.
Graph Databases Data is stored in nodes Neo4j
connected by edges. A
node is analogous to
an object.
Key/Value store Data is represented by Cassandra, BigTable
key/value pairs. A key
maye string, hash or
list.

5. Who Uses NoSQL Databases
 Google: BigTable
 Facebook: Cassandra
 LinkedIn: Voldemort
 Amazon: DynamoDB

6. References
 http://www.w3resource.com/mongodb
/nosql.php
 https://en.wikipedia.org/wiki/NoSQL
 http://newtech.about.com/od/databas
emanagement/a/Nosql.htm
 Few other resources in internet.

7. Thank you
 Please direct any
questions, corrections and comments
in the comments section.