2.11. Key Types
The logical and physical keys for a table can be classified by their behavior and their source. Table 2.1 is a quick table of my classification system.
Table 2.1. Classification System for Key Types
Natural Artificial "Exposed Surrogate Physical Locator" ===================================================================== Constructed from attributes | in the reality | of the data model | Y N N Y | Verifiable in reality | Y N N N | Verifiable in itself | Y Y N N | Visible to the user | Y Y Y N
2.11.1. Natural Keys
A natural key is a subset of attributes that occur in a table and act as a unique identifier. The user sees them. You can go to external reality and verify them. Examples of natural keys include the UPC codes on ...