A relational database is a database using tables of related data that is only stored once. Instead of repeating data, numerical links are made between them so the data isn’t repeated.

An entity is an individual thing about which data is stored.

An attribute is a piece of information about an entity stored as a field in a relational database. There are several kinds of attribute:

• A primary key is a kind of attribute that uniquely identifies each individual record.
• A composite primary key is a combination of attributes that uniquely identify each record.
• A foreign key is a primary key from another table.

Reference integrity is how if a primary key appears in one table it must appear in another.

A normalised database will either have a one-to-one, or a one-to-many relationship. Normalising database creates

Representing relationships

Crow’s feet are used to imply ‘many’ in this kind of diagram.