05. Normalisation and ER diagrams - revision mindmap
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Read the scenario
- What does one row represent?
- Entity facts versus relationship facts
- Business rules establish keys and cardinalities
- Keep every required attribute through decomposition
Functional dependencies
- Determinant → dependent
- A determines B does not mean B determines A
- Partial: proper part of composite key determines non-key fact
- Transitive: key → intermediate non-key fact → another non-key fact
Normal-form progression
- UNF: repeating group
- 1NF: atomic values, identifiable rows
- 2NF: remove partial non-key dependencies
- 3NF: remove relevant transitive non-key dependencies
ER relationships
- Read both directions
- 1:1, 1:M, M:N; cardinality versus optionality
- Foreign key on many side for 1:M
- Resolve M:N with linking entity and appropriate key
Worked decomposition
- Order header plus repeating products
- Flatten one row per order–product pair
- Separate Orders, Product and OrderLine
- Separate Customer; Quantity remains on OrderLine
Worked example & exam traps
- OrderLine key: (OrderID, ProductID); Quantity depends on the pair.
- ProductID → ProductName is partial: put it in Product.
- OrderID → CustomerID → CustomerName: separate Customer.
- Avoid: smaller tables automatically mean 3NF; names automatically identify
Sources and reading
This map condenses Chapter 05 and its source trail. Use the self-learning reading guide for the corresponding VJC pages and A notes. It does not add topics to the stated promo scope.