4 Types of NoSQL Databases with examples

[1] Document Databases

This is probably the most popular category of NoSQL databases.
Data is stored in JSON, BSON, or XML format.
A table is a collection of records. Records are known as documents
Documents can closely mimic the application domain object.
Examples - MongoDB, Couchbase, etc.

[2] Key Value Stores

Each element is stored as a key-value pair.
It's similar to relational DB but with only two columns - key & value.
The value can be an object.
Examples - Redis, DynamoDB

[3] Column-Oriented Databases

In RDBMS, Data is stored row by row.
But in Column-Oriented Database, data is stored as a set of columns.
More efficient for aggregation queries.
For example, find the total number of employees in a department.

Examples - MonetDB, Apache HBase

[4] Graph Databases

Graph DBs deal with relationships between data elements.
Each element is a node and it is connected to other elements.
They support different data formats such as JSON and key-value.
Not used as commonly as Document or Key-Value storage.

Examples - Neo4J, Amazon Neptune.