5. Entity Relationship Diagrams

These relationships can be shown in the form of a diagram.

This diagram is known as an 'entity relationship diagram', E-R diagram or ERD

As part of your exam, you will probably have to either draw or interpret an E-R diagram. Before you can do this, you need to be able to interpret the relationships between the entities.

These relationships take the form of:

- one-to-one

- one-to-many

- many-to-many

We will look at each of these relationships in turn over the next few pages.