Normalisation Flashcards
What is the process of normalisation in a relational database
Normalisation can be used to work out a complete database schema.
1: Define all relevant data to be stored and study connections:
2: Create an initial model/schema, e.g. using ER modelling.
3: Apply rules for normal forms (First Normal Form, Second, Third, Boyce-Codd Normal Form).
➢ 4: Change schema, decomposing tables until all tests pass (without losing any columns or (ideally) FDs along the way).
Explain the role Armstrong’s axioms play in the role of database design
These axioms, or more accurately, inference rules, allow you to do sophisticated work directly on functional dependencies, breaking them down, or adding new ones.
Armstrong’s Axioms provide inference powers to build algorithms and guarantee certain properties
SOUND: Given a set F specified on a relation R, any dependency we can infer from F using the 3 rules holds for every state r of R that satisfies the dependencies in F.
COMPLETE: We can use the 3 rules repeatedly to infer all possible dependencies that can be inferred from F
Explain, with the use of a suitable example, when denormalisation may be appropriate.
Denormalisation is the process of making compromises to the normalised tables by introducing intentional redundancy for performance reasons.
