Database Design Flashcards
K is super key of relation R iff
K ➡ R
A functional dependency is trivial if…
It is satisfied by all instances of a relation.
What is closure of F?
Set of all functional dependencies logically implied by F.
Name Armstrong’s Axioms.
Reflexivity
Augmentation
Transitivity
Give additional rules to Armstrong’s Axioms.
Union
Decomposition
Pseudo transitivity
Name some pitfalls of Relational Database Design.
Repetition of information.
Inability of represent certain information.
Give conditions for decomposition of a relation.
Lossless Decomposition
Dependency Preservation
What is normalisation?
A process of analysing the given relation schemes based on their FDs and primary keys to achieve the desirable properties.
Name two desirable properties of Normalization.
Minimising Redundancy.
Minimising Anomalies.
When is a relation in 1NF?
When all domains of all attributes of R are atomic.
When is a relation Schema in 2NF?
If every non prime attribute A in R is fully functionally dependent on the primary key of R.
When is a relation Schema in 3NF?
When a non trivial functional dependency X ➡ Y holds in R, either:
X is a super key of R
A is a prime attribute of R
When is a relation in BCNF?
If a FD X ➡ A holds in R, then X is super key of R.
When is a table in 4NF?
Iff for every one of its non trivial multivalued dependencies, X ➡➡ Y, X is a super key.
When is a table said to be in 5NF?
Iff every join dependency in it is implied by the candidate keys.
