- Natural key
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In relational model database design, a natural key is a candidate key that has a logical relationship to the attributes within that row. A natural key is sometimes called a domain key.
The main advantage of a natural key over a surrogate key, which has no such logical relationship, is that it already exists; there is no need to add a new, artificial column to the schema. Using a natural key (when one can be identified) also simplifies data quality: It ensures that there can only be one row for a key; this "one version of the truth" can be verified, because the natural key is based on a real-world observation.
The main disadvantage of choosing a natural key is that its value may change and the relational database engine may not be able to propagate that change across the related foreign keys. For example, if person_name is used as the primary key for the person table, and a person gets married and changes name, then all of the one-to-many related tables need to be updated also. The secondary disadvantage of choosing a natural key is identifying uniqueness. The primary key must consist of the attributes that uniquely identify a row. However, it may be difficult (or it may add constraints) to create a natural key on a table. For example, if person_name is used as a primary key for the person table, many persons may share the same name and all but the first entry will be rejected as a duplication. The uniqueness constraint may be overcome by adding an additional column to the primary key, like street_address, to increase the likelihood of uniqueness.
External links
- "Intelligent Versus Surrogate Keys", B Carter, http://www.bcarter.com/intsurr1.htm.
- "Avoid Unique Indexes – (Mistake 3 of 10)", Near Infinity, Create Data Disaster, http://www.nearinfinity.com/blogs/page/lrichard?entry=create_data_disaster_avoid_unique.
- Celko, Joseph ‘Joe’, "Keys and History", Intelligent Enterprise, http://www.intelligententerprise.com/030320/605celko1_1.jhtml.
- "Natural versus surrogate keys", c2, http://c2.com/cgi/wiki?AutoKeysVersusDomainKeys.
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