Identifier Attribute

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Natural Key

Set of Attributes K, whose values uniquely identify a Tuple of Relation is called Key. Each Relation must have one Key that helps to uniquely identify a Tuple of Relation. Relation can have more than one Key that is called Candidate Key.

Super Key is a set of attributes that uniquely identify a Record of Table in the Relational Database. An instance, Employee Table designed with {Emp_Code, Emp_Name, Designation, Phone, Salary, Dept_Code} attributes and the Record can identify through following Super Key {Emp_Code, Emp_Name, Designation} or {Emp_Code, Designation, Dept_Code} or {Emp_Code, Emp_Name, Dept_Code}.

Candidate Key is a minimal set of attributes that uniquely identify a Record of Table in the Relational Database. An instance, Employee Table designed with {Emp_Code, Emp_Name, Designation, Salary, Dept_Code} attributes and the Record can identify through following Candidate Key {Emp_Code, Phone} or {Emp_Code} or {Phone}.

Primary Key is an attribute that uniquely identifies a Record of Table in the Relational Database. Primary Key must define from Candidate Key of the Relation. An instance, {Emp_Code} attribute is a Primary Key of Employee Entity.

Composite Primary Key is a set of attributes that uniquely identifies a Record of Table in the Relational Database. Composite Primary Key must define from Candidate Key of the Relation. An instance, {Emp_Code, Phone} is a Composite Primary Key of Employee Entity.

Relation may have one or more Candidate Key. Primary Key and Composite Primary Key must define from one of the Candidate Key of Relation and the remaining Candidate Key is called Alternative Key. An instance, {Phone} is an Alternative Key of Employee Entity.

Foreign Key is used to define Referential Integrity Constrain with one attribute or set of attributes that reference a Referenced Key in the Relational Database. Referenced Key is used to define Referential Integrity Constraint with Unique or Primary Key that referenced by Foreign Key in the Relational Database.

Foreign Key must define in the Child Table and Unique or Primary Key must define in the Parent Table. An instance, EMPLOYEE is a Child Table that referenced DEPARTMENT Parent Table through common Dept_Code attribute. Relational Database Model authorizes to match the Foreign Key Data with Referenced Primary or Unique or Null Data.

Intelligent Key

Intelligent Key is formed with a combination of words with one Primary Key attribute that uniquely identifies a Record of Table in the Relational Database. An instance, Product_Code attribute is a 10 digits character data type that formed with a combination of Production Unit, Month of Manufacture, Year of Manufacture, Product Type and Product Code. First 2 characters are define Production Unit, Next 2 characters are define Month of Manufacture, Next 2 characters are define Year of Manufacture, Next 2 characters are define Product Type and Last 2 characters are define Product Code.

System Key

System Key is an Auto Generated Key that does not have any intelligence information, typically database is generate the System Key information with internal mechanism. System Key may define with Sequential Number or Random Number or Unique Information. System Key is used to uniquely identify a Record of Dependent Table in the Relational Database.

Database Management System is provides option to set a System Key with start and incremental data, when create a Table Object in the Relational Database. An instance, Product_Code is a 5 digits number that defined with Auto Generated Key with start and incremental data. When add new record in the particular Table, Database is add incremental and last System Key data and then update data in the Product_Code.

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