Databases are tools to manage data. The basic functions of a database are inserting, searching, updating, and deleting data, even though most database systems do more than this. Databases are classified into two different categories depending on how they store data: relational and nonrelational databases.

Relational databases structure data in a very detailed way, forcing the user to use a defined format and allowing the creation of connections—that is, relations—between different pieces of information. Nonrelational databases are systems that store data in a more relaxed way, as though there were no apparent structure. Even though with these very vague definitions you could assume that everybody would like to use relational databases, both systems are very useful; it just depends on how you want to use them.

In this book, we will focus on relational databases as they are widely used in small web applications, in which there are not huge amounts of data. The reason is...