Nøgletype

Nøgletype is a term used in Danish information management and database design to describe the category or function of a key used to identify records within a dataset or relational table. It is a metadata concept that helps describe how a key participates in data integrity and relationships.

Common nøgletype categories include primærnøgle (primary key), fremmednøgle (foreign key), kandidatløgle (candidate key), unik nøgle (unique key), sammensat nøgle (composite key), kunstig eller surrogate nøgle (surrogate key), and naturlig nøgle (natural key). A primærnøgle uniquely identifies each record in a table; a fremmednøgle refers to a key in another table to enforce a relationship; a kandidatnøgle is one of several attributes that could serve as a primary key; a unik nøgle must be unique but may allow nulls; a sammensat nøgle is formed from two or more attributes; a surrogate key is a system-generated identifier with no business meaning; a naturlig nøgle derives from the data’s real-world meaning.

In practice, nøgletype is documented in data dictionaries and entity-relationship diagrams to record the intended role, constraints, and referential behavior of each key. Choosing between natural and surrogate keys, for example, is a design decision that affects stability, update costs, and data integration. Referential integrity constraints typically reference the nøgletype to ensure consistent links between tables.

Example: In a customer database, CustomerID is the primærnøgle of the Customer table, while CustomerID in the Orders table is a fremmednøgle referencing Customer.CustomerID.

See also: database design, data dictionary, relational model, metadata.