Exploring relational databases

Relational databases are hardly a new idea. The idea was first introduced by Edgar F. Codd in 1970. Omitting the mathematical concepts behind it (for brevity), it says that data in a relational database is, as everybody knows, arranged into tables (we had a quick look at this in Chapter 7, Exploring Middleware and Frameworks, in the Persistence section).

Roughly speaking, each table can be seen as one of the objects in our business model, with the columns mapping to the object fields and the rows (also known as records) representing the different object instances.

In the following sections, we are going to review the basics of relational databases, starting with keys and relationships, the concept of transactionality, and stored procedures.

Keys and relationships

Depending on the database technology, it's a common idea to have a way to identify each row. This is commonly done by identifying a field (or a set of fields) that is unique...