The big idea: Normalising is not guesswork. It is the same four steps on any scenario.
List the data, make it atomic, remove partial dependencies, remove transitive ones. Follow them in order and 3NF falls out.
Do it on paper first: Write out a few sample rows with real values before touching tables.
Dependencies are much easier to see in actual data than in a list of column names.
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The four steps run end to end on a school scenario. Follow the same route on any other.
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1 — List every piece of data
2 — Reach 1NF
3 — Reach 2NF
4 — Reach 3NF
Then check it backwards: Take a fact you know the scenario needs — "which room does Mr Pinto use" — and follow the keys to find it.
If you cannot get there, a link is missing. If you find it twice, you are not in 3NF yet.
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The scenario: The hospital records which doctor saw which patient, on what date, in which ward, and which consultant heads that ward.
One wide table, and a few sample rows to reason over.
The unnormalised table
1NF and the key
2NF — the partial dependencies
3NF — the transitive dependency
The finished design: Patient (PatientID, PatientName) · Doctor (DoctorID, DoctorName) · Ward (WardID, WardName, ConsultantName) · Visit (PatientID, DoctorID, VisitDate, WardID).
Every fact now appears once. Change a ward's consultant and you change one row.
How this is tested — you must show the tables at each stage, with the keys marked. It comes up two ways:
Paper 1 Section A
- Construct a 3NF design from a scenario, 5-8 marks
- Show the tables and identify every key
- Justify a move you made
Paper 1 Section B — case study
- Normalise the case study's data
- Explain what problem each step removed
The classic trap: Jumping straight to a set of tables. Marks are awarded for the stages — showing 1NF, then 2NF, then 3NF — so a correct final answer with no working can still lose most of them.
A shop records: OrderID, OrderDate, CustomerID, CustomerName, ProductID, ProductName, UnitPrice, Quantity. Construct a design in 3NF.
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