Relational DBMS

We are going to spend a considerable amount of time on the Relational DBMS (RDBMS) model, so this tutorial is intended as brief introduction.

The RDBMS manages data (logically) as a collection of two-dimensional tables (e.g., a spreadsheet). Relationships between tables are maintained by having common values in each of the related tables and joining them together using relational algebra principles. That might sound like a mouthful, but in fact the concepts are very simple. Consider the following table of information/data about students:

As we can see, the table (also called a relation) looks very much like something we might see in spreadsheet. The columns of the table contain the individual specific information (or attributes) about the entity class (Student) we have chosen to keep data on. The rows (or tuples, a term which you might still hear but is becoming obsolete) are the individual entity instances (or, in our case, individual students, stored as records in the table). There is some additional terminology which we will (eventually) have to become familiar with:

We also noted that tables or relations are often linked or joined together:

In this case, we are able to join Table Student to Table Balance (using the common fields StudentID in Table Student and Student in Table Balance), Table Student to Table Department (using the common fields Major in Table Student and Depart in Table Department), and Table Balance to Table Department (using the common fields Department in Table Balance and Depart in Table Department).

If this sounds a little complex, don't worry: We will cover it in much greater detail in the next section.

??? So Relational models are better than either the Hierarchical or Network Models ???

Once again, not necessarily. As we getting tired of saying, life is a trade-off: