Normalisation

This lesson covers database normalisation for the OCR A-Level Computer Science (H446) specification. Normalisation is the process of organising a relational database to reduce redundancy and prevent anomalies.

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What is Normalisation?

Normalisation is a systematic process of organising the attributes and tables of a relational database to:

• Reduce data redundancy (storing the same data in multiple places).
• Eliminate insertion, update, and deletion anomalies.
• Ensure data integrity and consistency.
• Simplify queries and maintenance.

Normalisation is performed through a series of normal forms, each building on the previous one.

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Functional Dependencies

Before understanding normal forms, you need to understand functional dependencies.

A functional dependency exists when the value of one attribute (or set of attributes) determines the value of another attribute.

Written as: A -> B (A determines B)

Example: StudentID -> StudentName (knowing the StudentID uniquely determines the StudentName).

Notation	Meaning
A -> B	A functionally determines B
A -> B, C	A determines both B and C
A, B -> C	The combination of A and B determines C

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Unnormalised Form (UNF)