data normalisation NF

Question 1

1NF (first normal form)

Answer 1

• all data val are atomic (single cell holds single value)
• no repeating columns (if there are multiple columns used for the same purpose, eg math score, science score, columns are repeatedly used for scores, not 1NF)

Question 2

2NF (second normal form)

Answer 2

• non-key fields must be fully dependent on the (composite) PK (no partial dependency)
• since (field) do not depend on the complete PK, only on (one PK), it thus violates 2NF

Question 3

3NF (third normal form)

Answer 3

• (column) is transitively dependent on PK thru (other column). since transitive dependence violates 3NF, table is not in 3NF

Question 4

disadvantages of NOT using 3NF

Answer 4

less space available, anomalies in data

Question 5

advantages of using 3NF

Answer 5

takes up less space, changes only need to be made in one place vs multiple places in NOT 3NF (:. less error-prone)

Question 6

why not 3NF ? (when table not even in 1NF)

Answer 6

• 3NF req table to be in 2NF which req table to be in 1NF. 1NF req data vals to be atomic. since (column) contains multiple vals, data vals are not atomic. table is not in 3NF

Question 7

tips to read raw data (normalisation, NF)

Answer 7

• identify repeating datas (signals not normalised data, and should be placed in a separate table instead)
• identify combinations of data that seems unique to every row (these datas are all PKs, can have many PKs)