Normalisation

Question 1

What is normalisation?

Answer 1

Formal technique for analysing a relation based on its primary key and the functional dependencies between the attributes of that relation.

Question 2

What is lossless decomposition?

Answer 2

A decomposition is lossless if R1 union R2 -> (R1 || R2). AKA a join would provide the original relation

Question 3

When is a relation in 1NF?

Answer 3

Domains of all attributes in R are atomic, AKA indivisible units.

Question 4

When is a relation in 2NF?

Answer 4

Every non-prime attribute is fully functionally dependent on a candidate key (AKA candidate key identifies all attributes) and is in 1NF.

Question 5

How do we go from 1NF to 2NF?

Answer 5

Identify partial dependencies that exist on the primary key and remove them by placing them in a new relation

Question 6

When is a relation schema in 3NF?

Answer 6

When a non-trivial functional dependency X -> Y in R, at least one is true:
1. X is a superkey of R
2. Each attribute z in y-x is in candidate key of R.
AKA no transitive dependencies.

Question 7

When is a relational schema in BCNF?

Answer 7

When a non-trivial functional dependency X -> Y in R, X is a superkey of R