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At the most basic definition, "a key is a unique identifier", [1] so unique key is a pleonasm. Keys that are within their originating entity are unique within that entity. Keys that migrate to another entity may or may not be unique, depending on the design and how they are used in the other table.
A surrogate key (or synthetic key, pseudokey, entity identifier, factless key, or technical key [citation needed]) in a database is a unique identifier for either an entity in the modeled world or an object in the database. The surrogate key is not derived from application data, unlike a natural (or business) key. [1]
High-cardinality column values are typically identification numbers, email addresses, or user names. An example of a data table column with high-cardinality would be a USERS table with a column named USER_ID. This column would contain unique values of 1-n. Each time a new user is created in the USERS table, a new number would be created in the ...
CLASS words ideally would be a very short list of data types relevant to a particular application. Common CLASS words might be: NO (number), ID (identifier), TXT (text), AMT (amount), QTY (quantity), FL (flag), CD (code), W (work) and so forth. In practice, the available CLASS words would be a list of less than two dozen terms.
In database design, a persistent object identifier (POID) is a unique identifier of a record on a table, used as the primary key.Important characteristics of a POID are that it does not carry business information and are not generally exported or otherwise made visible to data users; as such a POID has many of the characteristics of a surrogate key.
A Uniform Resource Name (URN) is a Uniform Resource Identifier (URI) that uses the urn scheme.URNs are globally unique persistent identifiers assigned within defined namespaces so they will be available for a long period of time, even after the resource which they identify ceases to exist or becomes unavailable. [1]
Python has data classes which provides equality testing and can be made immutable using the frozen parameter. [21] It overrides the __str__ dunder method. [22] This example implementation includes a static method which can be used to initialize a new instance with a randomly generated universally unique identifier (UUID).
Each element in the weak entity set must have a relationship with exactly one element in the owner entity set, [1] and therefore, the relationship cannot be a many-to-many relationship. Two entities can be associated without either being classified as weak, even if one depends on the other, as long as each has its own unique attribute. [ 1 ]