Natural key

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A natural key (also known as business key [1] or domain key [2] ) is a type of unique key in a database formed of attributes that exist and are used in the external world outside the database (i.e. in the business domain or domain of discourse). [3] In the relational model of data, a natural key is a superkey and is therefore a functional determinant for all attributes in a relation.

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A natural key serves two complementary purposes:

The uniqueness constraint assures uniqueness of data within a certain technical context (e.g. a set of values in a table, file or relation variable) by rejecting input of any data that would otherwise violate the constraint. This means that the user can rely on a guaranteed correspondence between facts identified by key values recorded in a system and the external domain of discourse (a single version of the truth according to Kimball).

A natural key differs from a surrogate key which has no meaning outside the database itself and is not based on real-world observation or intended as a statement about the reality being modelled. A natural key therefore provides a certain data quality guarantee whereas a surrogate does not. It is common for elements of data to have several keys, any number of which may be natural or surrogate.

Advantages

The advantages of using a natural key to uniquely identify records in a relation include less disk space usage, the natural key is an attribute that is related to the business or the real world so in most cases, it is already being stored in the relation which saves disk space as compared to creating a new column for storing the surrogate key.

Another advantage of using natural keys is that it simplifies enforcement of data quality, and they are easier to relate to real life while designing the database system. They simplify the quality of data as using a natural key that is unique in the real world ensures that there cannot be multiple records with the same primary key. Comparing the database schema to a real world scenario is a huge part of designing a database schema and when a natural key is being used in the tables of the database, it makes it easy for the database engineer to engineer the database system.

Disadvantages

Usage of natural keys as unique identifiers in a table has one main disadvantage which is the change of business rules or the change of rules of the attribute in the real world. The definition of the structure of the natural key attribute might change in the future.

For example if there is a table storing the information about US citizens, the Social Security Number would act as the natural key, Social Security Number being the natural key might pose a problem in the future if the US government changes the structure of the Social Security Number and increases the number of digits in the SSN due to some reason. In that case, the database administrator will have to change the schema of the table and perhaps also update the records of the table. In other cases, this can prevent improvements of the system altogether due to too extensive effort required for the change, e.g., the inability of the knowledge management software Confluence, to represent multiple pages with the same title. [4]

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The relational model (RM) is an approach to managing data using a structure and language consistent with first-order predicate logic, first described in 1969 by English computer scientist Edgar F. Codd, where all data is represented in terms of tuples, grouped into relations. A database organized in terms of the relational model is a relational database.

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In relational database theory, a functional dependency is a constraint between two sets of attributes in a relation from a database. In other words, a functional dependency is a constraint between two attributes in a relation. Given a relation R and sets of attributes , X is said to functionally determineY if and only if each X value in R is associated with precisely one Y value in R; R is then said to satisfy the functional dependency X → Y. Equivalently, the projection is a function, i.e. Y is a function of X. In simple words, if the values for the X attributes are known, then the values for the Y attributes corresponding to x can be determined by looking them up in any tuple of R containing x. Customarily X is called the determinant set and Y the dependent set. A functional dependency FD: X → Y is called trivial if Y is a subset of X.

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In the relational model of databases, a primary key is a specific choice of a minimal set of attributes (columns) that uniquely specify a tuple (row) in a relation (table). Informally, a primary key is "which attributes identify a record," and in simple cases constitute a single attribute: a unique ID. More formally, a primary key is a choice of candidate key ; any other candidate key is an alternate key.

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In relational database management systems, a unique key is a candidate key. All the candidate keys of a relation can uniquely identify the records of the relation, but only one of them is used as the primary key of the relation. The remaining candidate keys are called unique keys because they can uniquely identify a record in a relation. Unique keys can consist of multiple columns. Unique keys are also called alternate keys. Unique keys are an alternative to the primary key of the relation. In SQL, the unique keys have a UNIQUE constraint assigned to them in order to prevent duplicates. Alternate keys may be used like the primary key when doing a single-table select or when filtering in a where clause, but are not typically used to join multiple tables.

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<span class="mw-page-title-main">Database model</span> Type of data model

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<span class="mw-page-title-main">Data vault modeling</span> Database modeling method

Data vault modeling is a database modeling method that is designed to provide long-term historical storage of data coming in from multiple operational systems. It is also a method of looking at historical data that deals with issues such as auditing, tracing of data, loading speed and resilience to change as well as emphasizing the need to trace where all the data in the database came from. This means that every row in a data vault must be accompanied by record source and load date attributes, enabling an auditor to trace values back to the source. The concept was published in 2000 by Dan Linstedt.

<span class="mw-page-title-main">Relation (database)</span>

In database theory, a relation, as originally defined by E. F. Codd, is a set of tuples (d1, d2, ..., dn), where each element dj is a member of Dj, a data domain. Codd's original definition notwithstanding, and contrary to the usual definition in mathematics, there is no ordering to the elements of the tuples of a relation. Instead, each element is termed an attribute value. An attribute is a name paired with a domain. An attribute value is an attribute name paired with an element of that attribute's domain, and a tuple is a set of attribute values in which no two distinct elements have the same name. Thus, in some accounts, a tuple is described as a function, mapping names to values.

The following is provided as an overview of and topical guide to databases:

References

  1. ↑ Data modelling: What exactly is a Business Key? by Roy, Rajiv Max. 19 November 2020. Retrieved 1 August 2022.
  2. ↑ Auto Keys Versus Domain Keys
  3. ↑ Intelligent Versus Surrogate Keys
  4. ↑ "[CONFSERVER-2524] Enable creation of same-named pages within a space - Create and track feature requests for Atlassian products".
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