1. Chapter 5
Terminology
A table is made out of records, records are made out of fields and fields are made out of
characters.
• The table (entity) must have a unique name
• Each field (attribute) must have a unique name
• Each record must be unique
• Each field must only contain a single data item
A record is a single row within a table
A field is an individual item within a record. Each field within a record should have unique
name. A field should only contain a single item of data.
A primary key allows a record in a table to be uniquely identified. Every value of the primary
key must be unique – e.g. Student ID number, passport number, barcode, ISBN number etc.
A simple key – is made up of a single field, e.g. student ID
A composite primary key combines more than one field to make a unique value
A secondary key is a field that is considered suitable for indexing the data, It is used to sort
the data in a different order to the primary key.
A foreign key is used to link tables together, a foreign key is a field in one table that is linked
to a primary key in another table. The data types of the linked fields must be the same
