Database definitions

Database Definitions:

AS ICT

A database is:

A collection of data or information which is held together in an organised or logical way.

A record is:

All of the data or information about one person or one thing.

A field is:

One piece of data or information about a person or thing.

Primary key:

The primary key is a field in a table which allows each record to be uniquely identified.

Flat-file database:

A database which contains only one table.

Data duplication:

Where data is unnecessarily repeated

Referential integrity:

Every foreign key value has a matching value in the corresponding primary key.  Referential integrity uses these to ensure that there are no orphan records i.e. it prevents you from deleting related records.

Foreign key – customer ID in rentals table, primary key – customer ID in customer table

Simple primary key:

A simple primary key is made up of a single field only e.g. customer number

Compound or composite primary key:

A compound / composite primary key combines more than one field to make a unique value.  e.g. each card in a deck would be identified by its suit and its value – Ace of Hearts

Foreign key:

A foreign key is used to link tables together and create a relationship. It is a field in one table that is linked to the primary key in another table