Introduction to Relational Databases

Relational Database Management Systems vs Database

There are two important concepts that are easy to confuse and they are used often. They are Relational Database Management System and Relational Database.

Relational Database Management System

Relational Database Management System (RDBMS) is software that is used to create and run databases. Once you install a RDBMS on your computer you can then create and run as many databases as you would like.

Common RDBMS

There are many RDBMS. Here are some common ones;
Free

• 
  MySQL
  
• 
  SQLite
  
• 
  PostgreSQL
  

Commercial (paid)

• 
  Oracle RDBMS (from Oracle)
  
• 
  DB2 (from IBM)
  
• 
  SQL Server (from Microsoft)
  

In this course we are going to use different RDBMS to give you experience. We are going to use free ones.

Relational Database

Once you have a DRBMS you can create databases. But the databases that you create can only run on that RDBMS.

Example

Let’s say that I work for a large corporation. We have four departments that need software: Accounting, Sales, Manufacturing and Shipping. We decided to purchase IBM’s DB2 and install it on our server. With it we create 4 databases, one for each department.

Analogy

A good analogy is Office Productivity software. Let’s say that I need to write 4 reports. I need to install an Office Productivity Suite once and then can create many documents. So, I install Microsoft Office and create 4 Word documents.