Normalisation

Seite 1

Unnormalised Form

- contain non-atomic data

- contain repeating groups and maybe redundant data

KEYWORDS

Non-atomic data = a field contains more than 1 item of data

Redundant data = unnecessarily repeated data

Seite 2

First normal Form

- all fields must contain atomic data

- there must be no repeating groups of data

- there must be a unique key

Seite 3

Second Normal Form

- must have no partial key dependencies

- only applies to tables with a compound key

Seite 4

Third Normal Form

- must have no non-key dependencies

- primary keys and all compound keys are ignored

Seite 5

Advantages and Disadvantages to Normalisation

Advantages

- can reduce size of database

- can reduce potential for errors

- searches can be carried our in index fields

- data can be look up from related tabled

- maintenance tasks can be completed more quickly

- database becomes more flexible

- data can fit onto one screen or one page more easily

Disadvantages

- can be difficult to understand data stored

- can be quite complex

- need to design the database and understand it properly