Normalisation Flashcards
What is normalisation?
A set of rules to reorganise relations to reduce redundancy and improve integrity
Why normalise data?
Get rid of data anomalies which cause data inconsistencies
What are the three different types of data anomalies?
- Insertion anomalies
- Deletion anomalies
- Update anomalies
What is a functional dependancy?
A constraint between two attributes where one attribute value (dependant) is determined by the other attribute value (determinant)
What is the determinant in a functional dependancy?
The attribute which uniquely identifies dependant
If a -> b, b is the dependant, a is the determinant
What is the invalid case in a function dependancy?
One to many relationship
What is a valid case in a functional dependancy?
Many to many
One to one
Many to one
What is a prime attribute?
An attribute which is part of the candidate key
What is a non-prime attribute?
An attribute which is not part of the candidate key
What is a partial dependancy?
A non-prime attribute that depends on part of the candidate key
What is a transitive dependancy?
A condition where A, B and C are attributes of a relation such that if A -> B and B -> C, then A -> C via B
What does A -> B mean?
B is functionally dependant on A
What are the steps to normalisation?
First normal form
Second normal form
Third normal form
Explain the characteristics of a relation in first normal form
Each row and column contains one and only one value
- No multivalued attributes
Explain the characteristics of a relation in second normal form
- In first normal form
- Any partial function dependancies are removed
- Non key attributes are identified by the whole primary key
