NoSQL means "not SQL." In a NoSQL database, there is no fixed schema. Data items are stored in key-value pairs, without strict relational organization like rows and columns.

This method resembles a hashmap. We will explore this further later in the article.

Object-Oriented Databases

Data stored in the form of an object is called an object-oriented database. We will discuss this further later in the article.

In-Memory Databases

In an in-memory database, data is stored directly in primary memory, such as RAM, rather than on secondary storage devices like hard disks or SSDs. Since it is stored in memory, it is called an In-Memory Database. We will look at this further later in the article.

Time-Series Databases

A time series database is used when our data consists of a series of events occurring at different time intervals. Events or time intervals are represented as time-value pairs.

Spatial Databases

This database handles data associated with physical space, often depicted in a two-dimensional (2D) format. Geometric space is stored and managed in these databases.

Multimedia Databases

This is a collection of data that includes text, images, graphics, and more.

Columnar Databases

In a columnar database, data is stored in columns, not rows.

XML Databases

In an XML database, data is stored in the form of XML.

NewSQL Databases

NewSQL databases fill the gaps between relational databases and NoSQL databases.

Blockchain Databases

In blockchain databases, data is stored in the form of blocks, representing a decentralized way of data storage.

In-Depth Look at Selected Databases

Relational Database

This is the most used database. These databases structure data into organized tables with predefined connections between them.

For instance, consider Table T1 and Table T2:

Both tables contain information about a person, creating a connection between them with interrelated data.

Data manipulation, like insert, update, and delete, is performed using SQL queries. Common databases include MySQL, PostgreSQL, Oracle, and Microsoft SQL Server.

NoSQL Database

NoSQL databases are designed to handle data that doesn’t fit neatly into traditional relational structures. Data isn’t stored in rows and columns, and traditional queries are not used.

For example, a key-value pair might look like this: Key: "Place", Value: "Mysore".

This structure resembles a hashmap, differing from relational databases that rely on structured tables and unique keys.

Object-Oriented Database

Object-oriented databases hold objects from Object-Oriented Programming (OOP). Everything is stored as objects, which are instances of classes. The combination of objects and classes forms an Object-Oriented Database.

These databases are particularly useful for applications with complex data designs, like scientific simulations and multimedia software.

In-Memory Database

In an In-Memory Database, data is stored in primary memory (RAM) instead of on a disk. This allows for faster data retrieval.

Since data is directly