Notes for A3.2.5 Differences Between Normal Forms - IB | RevisionDojo
A3.2.5 Differences Between Normal Forms Notes
Differences Between Normal Forms
Understanding Normal Forms
First Normal Form (1NF): Ensures that all data is atomic and that each table has a unique identifier.
Second Normal Form (2NF): Eliminates partial-key dependencies by ensuring that all non-key attributes depend on the entire primary key.
Third Normal Form (3NF): Removes transitive dependencies, ensuring that non-key attributes depend only on the primary key.
First Normal Form (1NF)
Repeating data is moved into a new entity.
Non-repeating data remains in its own entity and is given a primary key.
The primary key of the non-repeating entity is added to the new entity as a foreign key.
The new entity is assigned a unique identifier, usually a composite key.
Note
A common issue at this stage is partial key dependencies, where some attributes depend on only part of the composite key.
Partial dependencies violatenormalisation rules.
Second Normal Form (2NF)
Partial key dependencies are moved into their own entity.
A new primary key is assigned to that entity.
The original entity keeps the removed data’s key as both a primary and foreign key.
Note
The problem that remains is the presence of non-key (transitive)dependencies, attributes that do not rely on the key at all.
These still violate the normalisation principle.
Third Normal Form (3NF)
Transitive or non-key dependencies are moved into separate entities.
Each new entity is given its own primary key.
The new primary key becomes a foreign key in the entity it was removed from.
Note
Transitive dependencies can appear in any entity created earlier and must be removed.
Once transitive dependencies are eliminated, the structure complies fully with the normalisation principle.
Normalization Example for School Purchases
Unormalized Form
StudentID
StudentName
PurchaseDate
ItemsPurchased
PaymentMethod
101
Alice Smith
2024-05-10
Pen, Notebook
Card
102
Ben Wong
2024-05-11
Pencil
Cash
101
Alice Smith
2024-05-12
Ruler
Card
First Normal Form
Step 1: Make it Atomic
StudentID
StudentName
PurchaseDate
ItemsPurchased
PaymentMethod
101
Alice Smith
2024-05-10
Pen
Card
101
Alice Smith
2024-05-10
Notebook
Card
102
Ben Wong
2024-05-11
Pencil
Cash
101
Alice Smith
2024-05-12
Ruler
Card
Step 2: Remove Repeated Student Info
Student Table (PK: StudentID):
StudentID
StudentName
101
Alice Smith
102
Ben Wong
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Note
Introduction to Database Normalization
Database normalization is a systematic approach to organizing data in a database to reduce redundancy and improve data integrity.
The process involves breaking down tables into smaller, more manageable pieces while maintaining relationships between them.
Normalization follows a series of normal forms, each with specific rules and requirements.
AnalogyThink of normalization like organizing a messy closet. You start by grouping similar items together (1NF), then further organize them by category (2NF), and finally ensure everything has its proper place (3NF).
DefinitionNormalizationA process of organizing data in a database to minimize redundancy and dependency.
DefinitionNormal FormsA set of rules that define the level of normalization in a database table.
