Appendix A. Relational Database Technology: A Crash Course
ADO.NET can be used to access data from any data source: relational databases, object databases, flat files, and text files. The vast majority of web applications, however, will access data from a relational database such as SQL Server. While one can certainly write an entire book on relational databases and another on SQL, the essentials of these technologies are not hard to understand.
A database is a repository of data. A relational database organizes your data into tables that are "related" to one another. For example, one table might contain a customer's information and a second table might contain information about orders. The tables are related to one another because each customer has certain orders, and each order is owned by an individual customer.
Similarly, you might have a table of cars and a second table of car parts. Each part can be in one or more cars, and each car is made up of parts. Or, you might have a table for bugs and a table for developers. Each bug is owned by one developer, and each developer has a list of bugs he owns.