# Relational Database Notation

## Relational Notation versus ERD Diagrams

*Relational Database Notation* focuses on the physical modeling of a relational database.

The answer is that for some students relational notation will seem quite natural and for others it will take some getting used to.
I will continue to represent entities using both styles, so if you prefer graphics to relational notation you will have a visual reference to make the explanations more understandable.
All I ask is that you learn how to read relational notation. Doing so will allow you to study beyond this course and take advantage of resources that use *relational notation* to present their material.

*Domain:* Determines the type of data values that are permitted for that attribute.
*Primary key:* A field (or combination of fields) that uniquely identifies a record in a table.
*Foreign key:* A field (or combination of fields) used to link tables; a corresponding primary key field occurs in the same database.
*Data redundancy:* Duplication of data in a database.

## Defining Normal Forms the Academic Way

The following are the precise academic definitions of Normal Forms.
- 1st Normal Form (1NF):Eliminate repeating groups such that all records in all tables can be identified uniquely by a primary key in each table. In other words, all fields other than the primary key must depend on the primary key.
- 2nd Normal Form (2NF):All non-key values must be fully functionally dependent on the primary key. No partial dependencies are allowed. A partial dependency exists when a field is fully dependent on a part of a composite primary key.
- 3rd Normal Form (3NF):Eliminate transitive dependencies, meaning that a field is indirectly determined by the primary key. This is because the field is functionally dependent on another field, whereas the other field is dependent on the primary key.
- Boyce-Codd Normal Form (BCNF):Every determinant in a table is a candidate key. If there is only one candidate key, 3NF and BCNF are one and the same.
- 4th Normal Form (4NF):Eliminate multiple sets of multivalued dependencies.
- 5th Normal Form (5NF):Eliminate cyclic dependencies. 5NF is also known as Projection Normal Form (PJNF).
- Domain Key Normal Form (DKNF):DKNF is the ultimate application of normalization and is more a measurement of conceptual state, as opposed to a transformation process in itself.

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