In this model,the data is organized into tables (ie., rows and columns). These tables are called relations. A row in a table represents a relationship among a set of values.
Consider a sample database with three tables (relations), Suppliers, Items, Quantities:
- Suppliers (sup-no#,sup-name,status, city)
- Items ( item-no#, item-name, price)
- Quantities (sup-no#, item-no#, Qty)
- Rows of relations are generally referred to as tuples and the columns are usually referred to as attributes.
- No two tuples are identical and their ordering is not important.
- A relationship is represented by combining the primary key of the relations.
- Various operations can be performed on relations such as insert new tuples, delete tuples and modify tuples.
- There are several languages for expressing these operations. One such language is relational query language.