Databases are very important part of many applications nowadays. Quite many applications needs to handle data. There is a need to save and edit the data and search some special information from the data. Databases makes those operations much more easier than example textfiles.

There are several kind of database types and this site is focused on Relational databases.

A database is an organized collection of data for one or more purposes, usually in digital form. The data is typically organized to model relevant aspects of reality. The database may contain, for example, hospital patient data or institution grades and course informations.

The term "database" refers both to the way its users view it, and to the logical and physical materialization of its data, content, in files, computer memory, and computer data storage. This definition is very general, and is independent of the technology used. However, not every collection of data is a database; the term database implies that the data is managed to some level of quality (measured in terms of accuracy, availability, usability, and resilience) and this in turn often implies the use of a general-purpose Database management system (DBMS).

Here are some common requirements for the database:

• No redundant data: we don't have to save the same data to several places
• We can search the data using several conditions
• Using the data and the applications which will use it are independent about the physical structure of the database

DBMS is typically a complex software system that meets many usage requirements, and the databases that it maintains are often large and complex. The utilization of databases is now spread to such a wide degree that virtually every technology and product relies on databases and DBMSs for its development and commercialization, or even may have such embedded in it. Also, organizations and companies, from small to large, heavily depend on databases for their operations.

Some of the most popular DBMS's:

• MySQL and MariaDB
• PostgreSQL
• SQL Server (Microsoft)
• Oracle

The three leading open source implementations are MySQL, PostgreSQL and SQLite.

DBS = Database + DBMS

We can divide databases to two gategories based on how they are used.

Analytic databases are primarily static, read-only databases which store archived, historical data used for analysis. For example, a company might store sales records over the last ten years in an analytic database and use that database to analyze marketing strategies in relationship to demographics.

On the web, you will often see analytic databases in the form of inventory catalogs such as the one shown previously from Amazon.com. An inventory catalog analytical database usually holds descriptive information about all available products in the inventory.

Operational Databases on the other hand, are used to manage more dynamic bits of data. These types of databases allow you to do more than simply view archived data. Operational databases allow you to modify that data (add, change or delete data).

These types of databases are usually used to track real-time information. For example, a company might have an operational database used to track warehouse/stock quantities. As customers order products from an online web store, an operational database can be used to keep track of how many items have been sold and when the company will need to reorder stock.

Here is some examples of different kind of databases :

1. Hierarchical databases
2. Network databases
3. Relational databases (SQL databases)
4. Object-oriented databases
5. XML databases
6. NoSQL databases
7. Graph databases