Data Modeling - Identifier - (Primary|Natural|Surrogate|Business) key

1 - About

Every entity must have a key (also known as an identifier). A key is an attribute, or a group of attributes, which assumes a unique value for each entity instance.

A group of attributes that uniquely identifies an instance of an entity is called a concatenated key.

A primary key is that candidate key which will most commonly be used to uniquely identify a single entity instance.

Any candidate key that is not selected to become the primary key is called an alternate key.

3 - Example

  • database key,
  • URI,
  • National identification number

4 - Identifier

An identifier data type must be able to hold any key value.

A common implementation of this data type will be an integer. However, the column values can exceed the range of integer values supported by a 4-byte integer and other data type such as as 8-byte integer, decimal or character string may be needed.

5 - Keys

An Foreign Key is not a identifier but enforces a relationship. See Data Modeling - Foreign Key Constraint

5.1 - Primary

5.2 - Surrogate

5.3 - Natural

If the table has a true primary key – it is known as a “natural key”

5.4 - Business

Unique key that use the business users to identify uniquely an entity. The business key is a meaningful/business code based generally on the concatenation of attributes value of an entity instance.

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data_modeling/key.txt · Last modified: 2017/04/26 14:03 by gerardnico