First generation database systems
These are file based systems. Even though they are structured databases, they are using files in the backend. Each table is stored as a separate file. There is no relation between files (tables).
Among these, FoxPro was promoted by Microsoft and is still available in the market. The new form of FoxPro is called 'Visual FoxPro'.
The above systems allow data storage as well as programming against the data. For example, using FoxPro, you can save data as well as create fully functional FoxPro applications (This feature is not available in modern database systems like SQL Server).
Second generation database system
Microsoft introduced MS Access as a database system to compete with other industry leading database systems. MS Access is still file based, but all tables in a database is merged into one file. It is easy to move database into another place and all files are safe within the database.
MS Access allow you to store data as well as write fully functional applications. You can create rich applications with windows forms using MS Access.
Third generation database systems
SQL Server, Oracle, Sybase etc belong to this category. Even though data is still saved as file, you do not deal with them as files. You will always use an application called 'database server' to deal with the data. When you want to store or retrieve data, you will access the database server to do this job. You have to use a different application (like C#, VB.NET, C++) etc and communicate with the database server using some technology like ADO.NET.
In most cases, you will not even know where the database file is located. Instead, you will just need to know how to connect to the database server, user id, password etc. Once you are connected to the database server, you will send commands to the server to manipulate data.
Database servers understand a specific language called SQL. You will learn more about SQL in the upcoming chapters.