Normalisation

1NF

Atomic and Primary key

Each tuples (row) should atomic. And have a primary key attached.

| title                   | rating | genre                   |
|-------------------------|--------|-------------------------|
| The Martian             | 93     | drama, science fiction  |
| Guardians of the galaxy | 77     | comedy, science fiction |
| Star Wars               | 93     | action, science fiction |
| Brooklyn                | 98     | drama                   |

Genre is wrong - every value should be separate.

2NF

  • Be in 1NF
  • No partial function dependencies. (Look below)

All values should be relevant. - Order is wrong here, and should be a separate entry.

Wrong

Forkert

Great

Forkert

3NF

  • No transitive functional dependencies.

A query based on the Primary Key should only contain info regarding the same content.

CustomerID should not contain info regarding orders.

3NF

Data model

  1. Conceptual data model - draft ER diagram

  2. Logical data model - Uafhængig af tech. Detaljegrad lidt større

  3. Physical data model - Final, klar til at implementere

Crow's Foot Notation.

http://www2.cs.uregina.ca/~bernatja/crowsfoot.html

Functional Dependency

One column, depends on another.

The value of one column, is depending on another.

Partial functional dependency

A non-key column is dependent on some, but not all of the columns of the composite primary key.

    A non-key column is related to another non-key column


| city        | state         | st | population |
|-------------|---------------|----|------------|
| Santa Fe    | New Mexico    | NM | 67947      |
| Santa Fe    | Texas         | TX | 12222      |
| Springfield | Massachusetts | MA | 15360      |
| Springfield | Illinois      | IL | 11706      |

Partial If we change the state, we'll have to have the change the state abbreviation. State and st

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